FreeBSD/Linux Kernel Cross Reference
sys/net/netisr.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2007-2009 Robert N. M. Watson
      * Copyright (c) 2010-2011 Juniper Networks, Inc.
      * All rights reserved.
      *
      * This software was developed by Robert N. M. Watson under contract
      * to Juniper Networks, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    /*
     * netisr is a packet dispatch service, allowing synchronous (directly
     * dispatched) and asynchronous (deferred dispatch) processing of packets by
     * registered protocol handlers.  Callers pass a protocol identifier and
     * packet to netisr, along with a direct dispatch hint, and work will either
     * be immediately processed by the registered handler, or passed to a
     * software interrupt (SWI) thread for deferred dispatch.  Callers will
     * generally select one or the other based on:
     *
     * - Whether directly dispatching a netisr handler lead to code reentrance or
     *   lock recursion, such as entering the socket code from the socket code.
     * - Whether directly dispatching a netisr handler lead to recursive
     *   processing, such as when decapsulating several wrapped layers of tunnel
     *   information (IPSEC within IPSEC within ...).
     *
     * Maintaining ordering for protocol streams is a critical design concern.
     * Enforcing ordering limits the opportunity for concurrency, but maintains
     * the strong ordering requirements found in some protocols, such as TCP.  Of
     * related concern is CPU affinity--it is desirable to process all data
     * associated with a particular stream on the same CPU over time in order to
     * avoid acquiring locks associated with the connection on different CPUs,
     * keep connection data in one cache, and to generally encourage associated
     * user threads to live on the same CPU as the stream.  It's also desirable
     * to avoid lock migration and contention where locks are associated with
     * more than one flow.
     *
     * netisr supports several policy variations, represented by the
     * NETISR_POLICY_* constants, allowing protocols to play various roles in
     * identifying flows, assigning work to CPUs, etc.  These are described in
     * netisr.h.
     */
    
    #include "opt_ddb.h"
    #include "opt_device_polling.h"
    
    #include <sys/param.h>
    #include <sys/bus.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/malloc.h>
    #include <sys/interrupt.h>
    #include <sys/lock.h>
    #include <sys/mbuf.h>
    #include <sys/mutex.h>
    #include <sys/pcpu.h>
    #include <sys/proc.h>
    #include <sys/rmlock.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/socket.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    
    #ifdef DDB
    #include <ddb/ddb.h>
    #endif
    
    #define _WANT_NETISR_INTERNAL   /* Enable definitions from netisr_internal.h */
    #include <net/if.h>
    #include <net/if_var.h>
    #include <net/if_private.h>
    #include <net/netisr.h>
    #include <net/netisr_internal.h>
    #include <net/vnet.h>
   
   /*-
    * Synchronize use and modification of the registered netisr data structures;
    * acquire a read lock while modifying the set of registered protocols to
    * prevent partially registered or unregistered protocols from being run.
    *
    * The following data structures and fields are protected by this lock:
    *
    * - The netisr_proto array, including all fields of struct netisr_proto.
    * - The nws array, including all fields of struct netisr_worker.
    * - The nws_array array.
    *
    * Note: the NETISR_LOCKING define controls whether read locks are acquired
    * in packet processing paths requiring netisr registration stability.  This
    * is disabled by default as it can lead to measurable performance
    * degradation even with rmlocks (3%-6% for loopback ping-pong traffic), and
    * because netisr registration and unregistration is extremely rare at
    * runtime.  If it becomes more common, this decision should be revisited.
    *
    * XXXRW: rmlocks don't support assertions.
    */
   static struct rmlock    netisr_rmlock;
   #define NETISR_LOCK_INIT()      rm_init_flags(&netisr_rmlock, "netisr", \
                                       RM_NOWITNESS)
   #define NETISR_LOCK_ASSERT()
   #define NETISR_RLOCK(tracker)   rm_rlock(&netisr_rmlock, (tracker))
   #define NETISR_RUNLOCK(tracker) rm_runlock(&netisr_rmlock, (tracker))
   #define NETISR_WLOCK()          rm_wlock(&netisr_rmlock)
   #define NETISR_WUNLOCK()        rm_wunlock(&netisr_rmlock)
   /* #define      NETISR_LOCKING */
   
   static SYSCTL_NODE(_net, OID_AUTO, isr, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
       "netisr");
   
   /*-
    * Three global direct dispatch policies are supported:
    *
    * NETISR_DISPATCH_DEFERRED: All work is deferred for a netisr, regardless of
    * context (may be overridden by protocols).
    *
    * NETISR_DISPATCH_HYBRID: If the executing context allows direct dispatch,
    * and we're running on the CPU the work would be performed on, then direct
    * dispatch it if it wouldn't violate ordering constraints on the workstream.
    *
    * NETISR_DISPATCH_DIRECT: If the executing context allows direct dispatch,
    * always direct dispatch.  (The default.)
    *
    * Notice that changing the global policy could lead to short periods of
    * misordered processing, but this is considered acceptable as compared to
    * the complexity of enforcing ordering during policy changes.  Protocols can
    * override the global policy (when they're not doing that, they select
    * NETISR_DISPATCH_DEFAULT).
    */
   #define NETISR_DISPATCH_POLICY_DEFAULT  NETISR_DISPATCH_DIRECT
   #define NETISR_DISPATCH_POLICY_MAXSTR   20 /* Used for temporary buffers. */
   static u_int    netisr_dispatch_policy = NETISR_DISPATCH_POLICY_DEFAULT;
   static int      sysctl_netisr_dispatch_policy(SYSCTL_HANDLER_ARGS);
   SYSCTL_PROC(_net_isr, OID_AUTO, dispatch,
       CTLTYPE_STRING | CTLFLAG_RWTUN | CTLFLAG_NEEDGIANT,
       0, 0, sysctl_netisr_dispatch_policy, "A",
       "netisr dispatch policy");
   
   /*
    * Allow the administrator to limit the number of threads (CPUs) to use for
    * netisr.  We don't check netisr_maxthreads before creating the thread for
    * CPU 0. This must be set at boot. We will create at most one thread per CPU.
    * By default we initialize this to 1 which would assign just 1 cpu (cpu0) and
    * therefore only 1 workstream. If set to -1, netisr would use all cpus
    * (mp_ncpus) and therefore would have those many workstreams. One workstream
    * per thread (CPU).
    */
   static int      netisr_maxthreads = 1;          /* Max number of threads. */
   SYSCTL_INT(_net_isr, OID_AUTO, maxthreads, CTLFLAG_RDTUN,
       &netisr_maxthreads, 0,
       "Use at most this many CPUs for netisr processing");
   
   static int      netisr_bindthreads = 0;         /* Bind threads to CPUs. */
   SYSCTL_INT(_net_isr, OID_AUTO, bindthreads, CTLFLAG_RDTUN,
       &netisr_bindthreads, 0, "Bind netisr threads to CPUs.");
   
   /*
    * Limit per-workstream mbuf queue limits s to at most net.isr.maxqlimit,
    * both for initial configuration and later modification using
    * netisr_setqlimit().
    */
   #define NETISR_DEFAULT_MAXQLIMIT        10240
   static u_int    netisr_maxqlimit = NETISR_DEFAULT_MAXQLIMIT;
   SYSCTL_UINT(_net_isr, OID_AUTO, maxqlimit, CTLFLAG_RDTUN,
       &netisr_maxqlimit, 0,
       "Maximum netisr per-protocol, per-CPU queue depth.");
   
   /*
    * The default per-workstream mbuf queue limit for protocols that don't
    * initialize the nh_qlimit field of their struct netisr_handler.  If this is
    * set above netisr_maxqlimit, we truncate it to the maximum during boot.
    */
   #define NETISR_DEFAULT_DEFAULTQLIMIT    256
   static u_int    netisr_defaultqlimit = NETISR_DEFAULT_DEFAULTQLIMIT;
   SYSCTL_UINT(_net_isr, OID_AUTO, defaultqlimit, CTLFLAG_RDTUN,
       &netisr_defaultqlimit, 0,
       "Default netisr per-protocol, per-CPU queue limit if not set by protocol");
   
   /*
    * Store and export the compile-time constant NETISR_MAXPROT limit on the
    * number of protocols that can register with netisr at a time.  This is
    * required for crashdump analysis, as it sizes netisr_proto[].
    */
   static u_int    netisr_maxprot = NETISR_MAXPROT;
   SYSCTL_UINT(_net_isr, OID_AUTO, maxprot, CTLFLAG_RD,
       &netisr_maxprot, 0,
       "Compile-time limit on the number of protocols supported by netisr.");
   
   /*
    * The netisr_proto array describes all registered protocols, indexed by
    * protocol number.  See netisr_internal.h for more details.
    */
   static struct netisr_proto      netisr_proto[NETISR_MAXPROT];
   
   #ifdef VIMAGE
   /*
    * The netisr_enable array describes a per-VNET flag for registered
    * protocols on whether this netisr is active in this VNET or not.
    * netisr_register() will automatically enable the netisr for the
    * default VNET and all currently active instances.
    * netisr_unregister() will disable all active VNETs, including vnet0.
    * Individual network stack instances can be enabled/disabled by the
    * netisr_(un)register _vnet() functions.
    * With this we keep the one netisr_proto per protocol but add a
    * mechanism to stop netisr processing for vnet teardown.
    * Apart from that we expect a VNET to always be enabled.
    */
   VNET_DEFINE_STATIC(u_int,       netisr_enable[NETISR_MAXPROT]);
   #define V_netisr_enable         VNET(netisr_enable)
   #endif
   
   /*
    * Per-CPU workstream data.  See netisr_internal.h for more details.
    */
   DPCPU_DEFINE(struct netisr_workstream, nws);
   
   /*
    * Map contiguous values between 0 and nws_count into CPU IDs appropriate for
    * accessing workstreams.  This allows constructions of the form
    * DPCPU_ID_GET(nws_array[arbitraryvalue % nws_count], nws).
    */
   static u_int                             nws_array[MAXCPU];
   
   /*
    * Number of registered workstreams.  Will be at most the number of running
    * CPUs once fully started.
    */
   static u_int                             nws_count;
   SYSCTL_UINT(_net_isr, OID_AUTO, numthreads, CTLFLAG_RD,
       &nws_count, 0, "Number of extant netisr threads.");
   
   /*
    * Synchronization for each workstream: a mutex protects all mutable fields
    * in each stream, including per-protocol state (mbuf queues).  The SWI is
    * woken up if asynchronous dispatch is required.
    */
   #define NWS_LOCK(s)             mtx_lock(&(s)->nws_mtx)
   #define NWS_LOCK_ASSERT(s)      mtx_assert(&(s)->nws_mtx, MA_OWNED)
   #define NWS_UNLOCK(s)           mtx_unlock(&(s)->nws_mtx)
   #define NWS_SIGNAL(s)           swi_sched((s)->nws_swi_cookie, 0)
   
   /*
    * Utility routines for protocols that implement their own mapping of flows
    * to CPUs.
    */
   u_int
   netisr_get_cpucount(void)
   {
   
           return (nws_count);
   }
   
   u_int
   netisr_get_cpuid(u_int cpunumber)
   {
   
           return (nws_array[cpunumber % nws_count]);
   }
   
   /*
    * The default implementation of flow -> CPU ID mapping.
    *
    * Non-static so that protocols can use it to map their own work to specific
    * CPUs in a manner consistent to netisr for affinity purposes.
    */
   u_int
   netisr_default_flow2cpu(u_int flowid)
   {
   
           return (nws_array[flowid % nws_count]);
   }
   
   /*
    * Dispatch tunable and sysctl configuration.
    */
   struct netisr_dispatch_table_entry {
           u_int            ndte_policy;
           const char      *ndte_policy_str;
   };
   static const struct netisr_dispatch_table_entry netisr_dispatch_table[] = {
           { NETISR_DISPATCH_DEFAULT, "default" },
           { NETISR_DISPATCH_DEFERRED, "deferred" },
           { NETISR_DISPATCH_HYBRID, "hybrid" },
           { NETISR_DISPATCH_DIRECT, "direct" },
   };
   
   static void
   netisr_dispatch_policy_to_str(u_int dispatch_policy, char *buffer,
       u_int buflen)
   {
           const struct netisr_dispatch_table_entry *ndtep;
           const char *str;
           u_int i;
   
           str = "unknown";
           for (i = 0; i < nitems(netisr_dispatch_table); i++) {
                   ndtep = &netisr_dispatch_table[i];
                   if (ndtep->ndte_policy == dispatch_policy) {
                           str = ndtep->ndte_policy_str;
                           break;
                   }
           }
           snprintf(buffer, buflen, "%s", str);
   }
   
   static int
   netisr_dispatch_policy_from_str(const char *str, u_int *dispatch_policyp)
   {
           const struct netisr_dispatch_table_entry *ndtep;
           u_int i;
   
           for (i = 0; i < nitems(netisr_dispatch_table); i++) {
                   ndtep = &netisr_dispatch_table[i];
                   if (strcmp(ndtep->ndte_policy_str, str) == 0) {
                           *dispatch_policyp = ndtep->ndte_policy;
                           return (0);
                   }
           }
           return (EINVAL);
   }
   
   static int
   sysctl_netisr_dispatch_policy(SYSCTL_HANDLER_ARGS)
   {
           char tmp[NETISR_DISPATCH_POLICY_MAXSTR];
           size_t len;
           u_int dispatch_policy;
           int error;
   
           netisr_dispatch_policy_to_str(netisr_dispatch_policy, tmp,
               sizeof(tmp));
           /*
            * netisr is initialised very early during the boot when malloc isn't
            * available yet so we can't use sysctl_handle_string() to process
            * any non-default value that was potentially set via loader.
            */
           if (req->newptr != NULL) {
                   len = req->newlen - req->newidx;
                   if (len >= NETISR_DISPATCH_POLICY_MAXSTR)
                           return (EINVAL);
                   error = SYSCTL_IN(req, tmp, len);
                   if (error == 0) {
                           tmp[len] = '\0';
                           error = netisr_dispatch_policy_from_str(tmp,
                               &dispatch_policy);
                           if (error == 0 &&
                               dispatch_policy == NETISR_DISPATCH_DEFAULT)
                                   error = EINVAL;
                           if (error == 0)
                                   netisr_dispatch_policy = dispatch_policy;
                   }
           } else {
                   error = sysctl_handle_string(oidp, tmp, sizeof(tmp), req);
           }
           return (error);
   }
   
   /*
    * Register a new netisr handler, which requires initializing per-protocol
    * fields for each workstream.  All netisr work is briefly suspended while
    * the protocol is installed.
    */
   void
   netisr_register(const struct netisr_handler *nhp)
   {
           VNET_ITERATOR_DECL(vnet_iter);
           struct netisr_work *npwp;
           const char *name;
           u_int i, proto;
   
           proto = nhp->nh_proto;
           name = nhp->nh_name;
   
           /*
            * Test that the requested registration is valid.
            */
           KASSERT(nhp->nh_name != NULL,
               ("%s: nh_name NULL for %u", __func__, proto));
           KASSERT(nhp->nh_handler != NULL,
               ("%s: nh_handler NULL for %s", __func__, name));
           KASSERT(nhp->nh_policy == NETISR_POLICY_SOURCE ||
               nhp->nh_policy == NETISR_POLICY_FLOW ||
               nhp->nh_policy == NETISR_POLICY_CPU,
               ("%s: unsupported nh_policy %u for %s", __func__,
               nhp->nh_policy, name));
           KASSERT(nhp->nh_policy == NETISR_POLICY_FLOW ||
               nhp->nh_m2flow == NULL,
               ("%s: nh_policy != FLOW but m2flow defined for %s", __func__,
               name));
           KASSERT(nhp->nh_policy == NETISR_POLICY_CPU || nhp->nh_m2cpuid == NULL,
               ("%s: nh_policy != CPU but m2cpuid defined for %s", __func__,
               name));
           KASSERT(nhp->nh_policy != NETISR_POLICY_CPU || nhp->nh_m2cpuid != NULL,
               ("%s: nh_policy == CPU but m2cpuid not defined for %s", __func__,
               name));
           KASSERT(nhp->nh_dispatch == NETISR_DISPATCH_DEFAULT ||
               nhp->nh_dispatch == NETISR_DISPATCH_DEFERRED ||
               nhp->nh_dispatch == NETISR_DISPATCH_HYBRID ||
               nhp->nh_dispatch == NETISR_DISPATCH_DIRECT,
               ("%s: invalid nh_dispatch (%u)", __func__, nhp->nh_dispatch));
   
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u, %s): protocol too big", __func__, proto, name));
   
           /*
            * Test that no existing registration exists for this protocol.
            */
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_name == NULL,
               ("%s(%u, %s): name present", __func__, proto, name));
           KASSERT(netisr_proto[proto].np_handler == NULL,
               ("%s(%u, %s): handler present", __func__, proto, name));
   
           netisr_proto[proto].np_name = name;
           netisr_proto[proto].np_handler = nhp->nh_handler;
           netisr_proto[proto].np_m2flow = nhp->nh_m2flow;
           netisr_proto[proto].np_m2cpuid = nhp->nh_m2cpuid;
           netisr_proto[proto].np_drainedcpu = nhp->nh_drainedcpu;
           if (nhp->nh_qlimit == 0)
                   netisr_proto[proto].np_qlimit = netisr_defaultqlimit;
           else if (nhp->nh_qlimit > netisr_maxqlimit) {
                   printf("%s: %s requested queue limit %u capped to "
                       "net.isr.maxqlimit %u\n", __func__, name, nhp->nh_qlimit,
                       netisr_maxqlimit);
                   netisr_proto[proto].np_qlimit = netisr_maxqlimit;
           } else
                   netisr_proto[proto].np_qlimit = nhp->nh_qlimit;
           netisr_proto[proto].np_policy = nhp->nh_policy;
           netisr_proto[proto].np_dispatch = nhp->nh_dispatch;
           CPU_FOREACH(i) {
                   npwp = &(DPCPU_ID_PTR(i, nws))->nws_work[proto];
                   bzero(npwp, sizeof(*npwp));
                   npwp->nw_qlimit = netisr_proto[proto].np_qlimit;
           }
   
   #ifdef VIMAGE
           /*
            * Test that we are in vnet0 and have a curvnet set.
            */
           KASSERT(curvnet != NULL, ("%s: curvnet is NULL", __func__));
           KASSERT(IS_DEFAULT_VNET(curvnet), ("%s: curvnet %p is not vnet0 %p",
               __func__, curvnet, vnet0));
           VNET_LIST_RLOCK_NOSLEEP();
           VNET_FOREACH(vnet_iter) {
                   CURVNET_SET(vnet_iter);
                   V_netisr_enable[proto] = 1;
                   CURVNET_RESTORE();
           }
           VNET_LIST_RUNLOCK_NOSLEEP();
   #endif
           NETISR_WUNLOCK();
   }
   
   /*
    * Clear drop counters across all workstreams for a protocol.
    */
   void
   netisr_clearqdrops(const struct netisr_handler *nhp)
   {
           struct netisr_work *npwp;
   #ifdef INVARIANTS
           const char *name;
   #endif
           u_int i, proto;
   
           proto = nhp->nh_proto;
   #ifdef INVARIANTS
           name = nhp->nh_name;
   #endif
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, name));
   
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               name));
   
           CPU_FOREACH(i) {
                   npwp = &(DPCPU_ID_PTR(i, nws))->nws_work[proto];
                   npwp->nw_qdrops = 0;
           }
           NETISR_WUNLOCK();
   }
   
   /*
    * Query current drop counters across all workstreams for a protocol.
    */
   void
   netisr_getqdrops(const struct netisr_handler *nhp, u_int64_t *qdropp)
   {
           struct netisr_work *npwp;
           struct rm_priotracker tracker;
   #ifdef INVARIANTS
           const char *name;
   #endif
           u_int i, proto;
   
           *qdropp = 0;
           proto = nhp->nh_proto;
   #ifdef INVARIANTS
           name = nhp->nh_name;
   #endif
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, name));
   
           NETISR_RLOCK(&tracker);
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               name));
   
           CPU_FOREACH(i) {
                   npwp = &(DPCPU_ID_PTR(i, nws))->nws_work[proto];
                   *qdropp += npwp->nw_qdrops;
           }
           NETISR_RUNLOCK(&tracker);
   }
   
   /*
    * Query current per-workstream queue limit for a protocol.
    */
   void
   netisr_getqlimit(const struct netisr_handler *nhp, u_int *qlimitp)
   {
           struct rm_priotracker tracker;
   #ifdef INVARIANTS
           const char *name;
   #endif
           u_int proto;
   
           proto = nhp->nh_proto;
   #ifdef INVARIANTS
           name = nhp->nh_name;
   #endif
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, name));
   
           NETISR_RLOCK(&tracker);
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               name));
           *qlimitp = netisr_proto[proto].np_qlimit;
           NETISR_RUNLOCK(&tracker);
   }
   
   /*
    * Update the queue limit across per-workstream queues for a protocol.  We
    * simply change the limits, and don't drain overflowed packets as they will
    * (hopefully) take care of themselves shortly.
    */
   int
   netisr_setqlimit(const struct netisr_handler *nhp, u_int qlimit)
   {
           struct netisr_work *npwp;
   #ifdef INVARIANTS
           const char *name;
   #endif
           u_int i, proto;
   
           if (qlimit > netisr_maxqlimit)
                   return (EINVAL);
   
           proto = nhp->nh_proto;
   #ifdef INVARIANTS
           name = nhp->nh_name;
   #endif
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, name));
   
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               name));
   
           netisr_proto[proto].np_qlimit = qlimit;
           CPU_FOREACH(i) {
                   npwp = &(DPCPU_ID_PTR(i, nws))->nws_work[proto];
                   npwp->nw_qlimit = qlimit;
           }
           NETISR_WUNLOCK();
           return (0);
   }
   
   /*
    * Drain all packets currently held in a particular protocol work queue.
    */
   static void
   netisr_drain_proto(struct netisr_work *npwp)
   {
           struct mbuf *m;
   
           /*
            * We would assert the lock on the workstream but it's not passed in.
            */
           while ((m = npwp->nw_head) != NULL) {
                   npwp->nw_head = m->m_nextpkt;
                   m->m_nextpkt = NULL;
                   if (npwp->nw_head == NULL)
                           npwp->nw_tail = NULL;
                   npwp->nw_len--;
                   m_freem(m);
           }
           KASSERT(npwp->nw_tail == NULL, ("%s: tail", __func__));
           KASSERT(npwp->nw_len == 0, ("%s: len", __func__));
   }
   
   /*
    * Remove the registration of a network protocol, which requires clearing
    * per-protocol fields across all workstreams, including freeing all mbufs in
    * the queues at time of unregister.  All work in netisr is briefly suspended
    * while this takes place.
    */
   void
   netisr_unregister(const struct netisr_handler *nhp)
   {
           VNET_ITERATOR_DECL(vnet_iter);
           struct netisr_work *npwp;
   #ifdef INVARIANTS
           const char *name;
   #endif
           u_int i, proto;
   
           proto = nhp->nh_proto;
   #ifdef INVARIANTS
           name = nhp->nh_name;
   #endif
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, name));
   
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               name));
   
   #ifdef VIMAGE
           VNET_LIST_RLOCK_NOSLEEP();
           VNET_FOREACH(vnet_iter) {
                   CURVNET_SET(vnet_iter);
                   V_netisr_enable[proto] = 0;
                   CURVNET_RESTORE();
           }
           VNET_LIST_RUNLOCK_NOSLEEP();
   #endif
   
           netisr_proto[proto].np_name = NULL;
           netisr_proto[proto].np_handler = NULL;
           netisr_proto[proto].np_m2flow = NULL;
           netisr_proto[proto].np_m2cpuid = NULL;
           netisr_proto[proto].np_qlimit = 0;
           netisr_proto[proto].np_policy = 0;
           CPU_FOREACH(i) {
                   npwp = &(DPCPU_ID_PTR(i, nws))->nws_work[proto];
                   netisr_drain_proto(npwp);
                   bzero(npwp, sizeof(*npwp));
           }
           NETISR_WUNLOCK();
   }
   
   #ifdef VIMAGE
   void
   netisr_register_vnet(const struct netisr_handler *nhp)
   {
           u_int proto;
   
           proto = nhp->nh_proto;
   
           KASSERT(curvnet != NULL, ("%s: curvnet is NULL", __func__));
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, nhp->nh_name));
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               nhp->nh_name));
   
           V_netisr_enable[proto] = 1;
           NETISR_WUNLOCK();
   }
   
   static void
   netisr_drain_proto_vnet(struct vnet *vnet, u_int proto)
   {
           struct epoch_tracker et;
           struct netisr_workstream *nwsp;
           struct netisr_work *npwp;
           struct mbuf *m, *mp, *n, *ne;
           struct ifnet *ifp;
           u_int i;
   
           KASSERT(vnet != NULL, ("%s: vnet is NULL", __func__));
           NETISR_LOCK_ASSERT();
   
           CPU_FOREACH(i) {
                   nwsp = DPCPU_ID_PTR(i, nws);
                   if (nwsp->nws_intr_event == NULL)
                           continue;
                   npwp = &nwsp->nws_work[proto];
                   NWS_LOCK(nwsp);
   
                   /*
                    * Rather than dissecting and removing mbufs from the middle
                    * of the chain, we build a new chain if the packet stays and
                    * update the head and tail pointers at the end.  All packets
                    * matching the given vnet are freed.
                    */
                   m = npwp->nw_head;
                   n = ne = NULL;
                   NET_EPOCH_ENTER(et);
                   while (m != NULL) {
                           mp = m;
                           m = m->m_nextpkt;
                           mp->m_nextpkt = NULL;
                           if ((ifp = ifnet_byindexgen(mp->m_pkthdr.rcvidx,
                               mp->m_pkthdr.rcvgen)) != NULL &&
                               ifp->if_vnet != vnet) {
                                   if (n == NULL) {
                                           n = ne = mp;
                                   } else {
                                           ne->m_nextpkt = mp;
                                           ne = mp;
                                   }
                                   continue;
                           }
                           /* This is a packet in the selected vnet, or belongs
                              to destroyed interface. Free it. */
                           npwp->nw_len--;
                           m_freem(mp);
                   }
                   NET_EPOCH_EXIT(et);
                   npwp->nw_head = n;
                   npwp->nw_tail = ne;
                   NWS_UNLOCK(nwsp);
           }
   }
   
   void
   netisr_unregister_vnet(const struct netisr_handler *nhp)
   {
           u_int proto;
   
           proto = nhp->nh_proto;
   
           KASSERT(curvnet != NULL, ("%s: curvnet is NULL", __func__));
           KASSERT(proto < NETISR_MAXPROT,
               ("%s(%u): protocol too big for %s", __func__, proto, nhp->nh_name));
           NETISR_WLOCK();
           KASSERT(netisr_proto[proto].np_handler != NULL,
               ("%s(%u): protocol not registered for %s", __func__, proto,
               nhp->nh_name));
   
           V_netisr_enable[proto] = 0;
   
           netisr_drain_proto_vnet(curvnet, proto);
           NETISR_WUNLOCK();
   }
   #endif
   
   /*
    * Compose the global and per-protocol policies on dispatch, and return the
    * dispatch policy to use.
    */
   static u_int
   netisr_get_dispatch(struct netisr_proto *npp)
   {
   
           /*
            * Protocol-specific configuration overrides the global default.
            */
           if (npp->np_dispatch != NETISR_DISPATCH_DEFAULT)
                   return (npp->np_dispatch);
           return (netisr_dispatch_policy);
   }
   
   /*
    * Look up the workstream given a packet and source identifier.  Do this by
    * checking the protocol's policy, and optionally call out to the protocol
    * for assistance if required.
    */
   static struct mbuf *
   netisr_select_cpuid(struct netisr_proto *npp, u_int dispatch_policy,
       uintptr_t source, struct mbuf *m, u_int *cpuidp)
   {
           struct ifnet *ifp;
           u_int policy;
   
           NETISR_LOCK_ASSERT();
   
           /*
            * In the event we have only one worker, shortcut and deliver to it
            * without further ado.
            */
           if (nws_count == 1) {
                   *cpuidp = nws_array[0];
                   return (m);
           }
   
           /*
            * What happens next depends on the policy selected by the protocol.
            * If we want to support per-interface policies, we should do that
            * here first.
            */
           policy = npp->np_policy;
           if (policy == NETISR_POLICY_CPU) {
                   m = npp->np_m2cpuid(m, source, cpuidp);
                   if (m == NULL)
                           return (NULL);
   
                   /*
                    * It's possible for a protocol not to have a good idea about
                    * where to process a packet, in which case we fall back on
                    * the netisr code to decide.  In the hybrid case, return the
                    * current CPU ID, which will force an immediate direct
                    * dispatch.  In the queued case, fall back on the SOURCE
                    * policy.
                    */
                   if (*cpuidp != NETISR_CPUID_NONE) {
                           *cpuidp = netisr_get_cpuid(*cpuidp);
                           return (m);
                   }
                   if (dispatch_policy == NETISR_DISPATCH_HYBRID) {
                           *cpuidp = netisr_get_cpuid(curcpu);
                           return (m);
                   }
                   policy = NETISR_POLICY_SOURCE;
           }
   
           if (policy == NETISR_POLICY_FLOW) {
                   if (M_HASHTYPE_GET(m) == M_HASHTYPE_NONE &&
                       npp->np_m2flow != NULL) {
                           m = npp->np_m2flow(m, source);
                           if (m == NULL)
                                   return (NULL);
                   }
                   if (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) {
                           *cpuidp =
                               netisr_default_flow2cpu(m->m_pkthdr.flowid);
                           return (m);
                   }
                   policy = NETISR_POLICY_SOURCE;
           }
   
           KASSERT(policy == NETISR_POLICY_SOURCE,
               ("%s: invalid policy %u for %s", __func__, npp->np_policy,
               npp->np_name));
   
           MPASS((m->m_pkthdr.csum_flags & CSUM_SND_TAG) == 0);
           ifp = m->m_pkthdr.rcvif;
           if (ifp != NULL)
                   *cpuidp = nws_array[(ifp->if_index + source) % nws_count];
           else
                   *cpuidp = nws_array[source % nws_count];
           return (m);
   }
   
   /*
    * Process packets associated with a workstream and protocol.  For reasons of
    * fairness, we process up to one complete netisr queue at a time, moving the
    * queue to a stack-local queue for processing, but do not loop refreshing
    * from the global queue.  The caller is responsible for deciding whether to
    * loop, and for setting the NWS_RUNNING flag.  The passed workstream will be
    * locked on entry and relocked before return, but will be released while
    * processing.  The number of packets processed is returned.
    */
   static u_int
   netisr_process_workstream_proto(struct netisr_workstream *nwsp, u_int proto)
   {
           struct netisr_work local_npw, *npwp;
           u_int handled;
           struct mbuf *m;
   
           NETISR_LOCK_ASSERT();
           NWS_LOCK_ASSERT(nwsp);
   
           KASSERT(nwsp->nws_flags & NWS_RUNNING,
               ("%s(%u): not running", __func__, proto));
           KASSERT(proto >= 0 && proto < NETISR_MAXPROT,
               ("%s(%u): invalid proto\n", __func__, proto));
   
           npwp = &nwsp->nws_work[proto];
           if (npwp->nw_len == 0)
                   return (0);
   
           /*
            * Move the global work queue to a thread-local work queue.
            *
            * Notice that this means the effective maximum length of the queue
            * is actually twice that of the maximum queue length specified in
            * the protocol registration call.
            */
           handled = npwp->nw_len;
           local_npw = *npwp;
           npwp->nw_head = NULL;
           npwp->nw_tail = NULL;
           npwp->nw_len = 0;
           nwsp->nws_pendingbits &= ~(1 << proto);
           NWS_UNLOCK(nwsp);
           while ((m = local_npw.nw_head) != NULL) {
                   local_npw.nw_head = m->m_nextpkt;
                   m->m_nextpkt = NULL;
                   if (local_npw.nw_head == NULL)
                           local_npw.nw_tail = NULL;
                   local_npw.nw_len--;
                   if (__predict_false(m_rcvif_restore(m) == NULL)) {
                           m_freem(m);
                           continue;
                   }
                   CURVNET_SET(m->m_pkthdr.rcvif->if_vnet);
                   netisr_proto[proto].np_handler(m);
                   CURVNET_RESTORE();
           }
           KASSERT(local_npw.nw_len == 0,
               ("%s(%u): len %u", __func__, proto, local_npw.nw_len));
           if (netisr_proto[proto].np_drainedcpu)
                   netisr_proto[proto].np_drainedcpu(nwsp->nws_cpu);
           NWS_LOCK(nwsp);
           npwp->nw_handled += handled;
           return (handled);
   }
   
   /*
    * SWI handler for netisr -- processes packets in a set of workstreams that
    * it owns, woken up by calls to NWS_SIGNAL().  If this workstream is already
    * being direct dispatched, go back to sleep and wait for the dispatching
    * thread to wake us up again.
    */
   static void
   swi_net(void *arg)
   {
   #ifdef NETISR_LOCKING
           struct rm_priotracker tracker;
   #endif
           struct netisr_workstream *nwsp;
           u_int bits, prot;
   
           nwsp = arg;
   
   #ifdef DEVICE_POLLING
           KASSERT(nws_count == 1,
               ("%s: device_polling but nws_count != 1", __func__));
           netisr_poll();
   #endif
   #ifdef NETISR_LOCKING
           NETISR_RLOCK(&tracker);
   #endif
           NWS_LOCK(nwsp);
           KASSERT(!(nwsp->nws_flags & NWS_RUNNING), ("swi_net: running"));
           if (nwsp->nws_flags & NWS_DISPATCHING)
                   goto out;
           nwsp->nws_flags |= NWS_RUNNING;
           nwsp->nws_flags &= ~NWS_SCHEDULED;
           while ((bits = nwsp->nws_pendingbits) != 0) {
                   while ((prot = ffs(bits)) != 0) {
                           prot--;
                           bits &= ~(1 << prot);
                           (void)netisr_process_workstream_proto(nwsp, prot);
                   }
           }
           nwsp->nws_flags &= ~NWS_RUNNING;
   out:
           NWS_UNLOCK(nwsp);
   #ifdef NETISR_LOCKING
           NETISR_RUNLOCK(&tracker);
   #endif
   #ifdef DEVICE_POLLING
           netisr_pollmore();
   #endif
   }
   
   static int
   netisr_queue_workstream(struct netisr_workstream *nwsp, u_int proto,
       struct netisr_work *npwp, struct mbuf *m, int *dosignalp)
   {
   
           NWS_LOCK_ASSERT(nwsp);
   
           *dosignalp = 0;
           if (npwp->nw_len < npwp->nw_qlimit) {
                   m_rcvif_serialize(m);
                  m->m_nextpkt = NULL;
                  if (npwp->nw_head == NULL) {
                          npwp->nw_head = m;
                          npwp->nw_tail = m;
                  } else {
                          npwp->nw_tail->m_nextpkt = m;
                          npwp->nw_tail = m;
                  }
                  npwp->nw_len++;
                  if (npwp->nw_len > npwp->nw_watermark)
                          npwp->nw_watermark = npwp->nw_len;
  
                  /*
                   * We must set the bit regardless of NWS_RUNNING, so that
                   * swi_net() keeps calling netisr_process_workstream_proto().
                   */
                  nwsp->nws_pendingbits |= (1 << proto);
                  if (!(nwsp->nws_flags & 
                      (NWS_RUNNING | NWS_DISPATCHING | NWS_SCHEDULED))) {
                          nwsp->nws_flags |= NWS_SCHEDULED;
                          *dosignalp = 1; /* Defer until unlocked. */
                  }
                  npwp->nw_queued++;
                  return (0);
          } else {
                  m_freem(m);
                  npwp->nw_qdrops++;
                  return (ENOBUFS);
          }
  }
  
  static int
  netisr_queue_internal(u_int proto, struct mbuf *m, u_int cpuid)
  {
          struct netisr_workstream *nwsp;
          struct netisr_work *npwp;
          int dosignal, error;
  
  #ifdef NETISR_LOCKING
          NETISR_LOCK_ASSERT();
  #endif
          KASSERT(cpuid <= mp_maxid, ("%s: cpuid too big (%u, %u)", __func__,
              cpuid, mp_maxid));
          KASSERT(!CPU_ABSENT(cpuid), ("%s: CPU %u absent", __func__, cpuid));
  
          dosignal = 0;
          error = 0;
          nwsp = DPCPU_ID_PTR(cpuid, nws);
          npwp = &nwsp->nws_work[proto];
          NWS_LOCK(nwsp);
          error = netisr_queue_workstream(nwsp, proto, npwp, m, &dosignal);
          NWS_UNLOCK(nwsp);
          if (dosignal)
                  NWS_SIGNAL(nwsp);
          return (error);
  }
  
  int
  netisr_queue_src(u_int proto, uintptr_t source, struct mbuf *m)
  {
  #ifdef NETISR_LOCKING
          struct rm_priotracker tracker;
  #endif
          u_int cpuid;
          int error;
  
          KASSERT(proto < NETISR_MAXPROT,
              ("%s: invalid proto %u", __func__, proto));
  
  #ifdef NETISR_LOCKING
          NETISR_RLOCK(&tracker);
  #endif
          KASSERT(netisr_proto[proto].np_handler != NULL,
              ("%s: invalid proto %u", __func__, proto));
  
  #ifdef VIMAGE
          if (V_netisr_enable[proto] == 0) {
                  m_freem(m);
                  return (ENOPROTOOPT);
          }
  #endif
  
          m = netisr_select_cpuid(&netisr_proto[proto], NETISR_DISPATCH_DEFERRED,
              source, m, &cpuid);
          if (m != NULL) {
                  KASSERT(!CPU_ABSENT(cpuid), ("%s: CPU %u absent", __func__,
                      cpuid));
                  VNET_ASSERT(m->m_pkthdr.rcvif != NULL,
                      ("%s:%d rcvif == NULL: m=%p", __func__, __LINE__, m));
                  error = netisr_queue_internal(proto, m, cpuid);
          } else
                  error = ENOBUFS;
  #ifdef NETISR_LOCKING
          NETISR_RUNLOCK(&tracker);
  #endif
          return (error);
  }
  
  int
  netisr_queue(u_int proto, struct mbuf *m)
  {
  
          return (netisr_queue_src(proto, 0, m));
  }
  
  /*
   * Dispatch a packet for netisr processing; direct dispatch is permitted by
   * calling context.
   */
  int
  netisr_dispatch_src(u_int proto, uintptr_t source, struct mbuf *m)
  {
  #ifdef NETISR_LOCKING
          struct rm_priotracker tracker;
  #endif
          struct netisr_workstream *nwsp;
          struct netisr_proto *npp;
          struct netisr_work *npwp;
          int dosignal, error;
          u_int cpuid, dispatch_policy;
  
          NET_EPOCH_ASSERT();
          KASSERT(proto < NETISR_MAXPROT,
              ("%s: invalid proto %u", __func__, proto));
  #ifdef NETISR_LOCKING
          NETISR_RLOCK(&tracker);
  #endif
          npp = &netisr_proto[proto];
          KASSERT(npp->np_handler != NULL, ("%s: invalid proto %u", __func__,
              proto));
  
  #ifdef VIMAGE
          if (V_netisr_enable[proto] == 0) {
                  m_freem(m);
                  return (ENOPROTOOPT);
          }
  #endif
  
          dispatch_policy = netisr_get_dispatch(npp);
          if (dispatch_policy == NETISR_DISPATCH_DEFERRED)
                  return (netisr_queue_src(proto, source, m));
  
          /*
           * If direct dispatch is forced, then unconditionally dispatch
           * without a formal CPU selection.  Borrow the current CPU's stats,
           * even if there's no worker on it.  In this case we don't update
           * nws_flags because all netisr processing will be source ordered due
           * to always being forced to directly dispatch.
           */
          if (dispatch_policy == NETISR_DISPATCH_DIRECT) {
                  nwsp = DPCPU_PTR(nws);
                  npwp = &nwsp->nws_work[proto];
                  npwp->nw_dispatched++;
                  npwp->nw_handled++;
                  netisr_proto[proto].np_handler(m);
                  error = 0;
                  goto out_unlock;
          }
  
          KASSERT(dispatch_policy == NETISR_DISPATCH_HYBRID,
              ("%s: unknown dispatch policy (%u)", __func__, dispatch_policy));
  
          /*
           * Otherwise, we execute in a hybrid mode where we will try to direct
           * dispatch if we're on the right CPU and the netisr worker isn't
           * already running.
           */
          sched_pin();
          m = netisr_select_cpuid(&netisr_proto[proto], NETISR_DISPATCH_HYBRID,
              source, m, &cpuid);
          if (m == NULL) {
                  error = ENOBUFS;
                  goto out_unpin;
          }
          KASSERT(!CPU_ABSENT(cpuid), ("%s: CPU %u absent", __func__, cpuid));
          if (cpuid != curcpu)
                  goto queue_fallback;
          nwsp = DPCPU_PTR(nws);
          npwp = &nwsp->nws_work[proto];
  
          /*-
           * We are willing to direct dispatch only if three conditions hold:
           *
           * (1) The netisr worker isn't already running,
           * (2) Another thread isn't already directly dispatching, and
           * (3) The netisr hasn't already been woken up.
           */
          NWS_LOCK(nwsp);
          if (nwsp->nws_flags & (NWS_RUNNING | NWS_DISPATCHING | NWS_SCHEDULED)) {
                  error = netisr_queue_workstream(nwsp, proto, npwp, m,
                      &dosignal);
                  NWS_UNLOCK(nwsp);
                  if (dosignal)
                          NWS_SIGNAL(nwsp);
                  goto out_unpin;
          }
  
          /*
           * The current thread is now effectively the netisr worker, so set
           * the dispatching flag to prevent concurrent processing of the
           * stream from another thread (even the netisr worker), which could
           * otherwise lead to effective misordering of the stream.
           */
          nwsp->nws_flags |= NWS_DISPATCHING;
          NWS_UNLOCK(nwsp);
          netisr_proto[proto].np_handler(m);
          NWS_LOCK(nwsp);
          nwsp->nws_flags &= ~NWS_DISPATCHING;
          npwp->nw_handled++;
          npwp->nw_hybrid_dispatched++;
  
          /*
           * If other work was enqueued by another thread while we were direct
           * dispatching, we need to signal the netisr worker to do that work.
           * In the future, we might want to do some of that work in the
           * current thread, rather than trigger further context switches.  If
           * so, we'll want to establish a reasonable bound on the work done in
           * the "borrowed" context.
           */
          if (nwsp->nws_pendingbits != 0) {
                  nwsp->nws_flags |= NWS_SCHEDULED;
                  dosignal = 1;
          } else
                  dosignal = 0;
          NWS_UNLOCK(nwsp);
          if (dosignal)
                  NWS_SIGNAL(nwsp);
          error = 0;
          goto out_unpin;
  
  queue_fallback:
          error = netisr_queue_internal(proto, m, cpuid);
  out_unpin:
          sched_unpin();
  out_unlock:
  #ifdef NETISR_LOCKING
          NETISR_RUNLOCK(&tracker);
  #endif
          return (error);
  }
  
  int
  netisr_dispatch(u_int proto, struct mbuf *m)
  {
  
          return (netisr_dispatch_src(proto, 0, m));
  }
  
  #ifdef DEVICE_POLLING
  /*
   * Kernel polling borrows a netisr thread to run interface polling in; this
   * function allows kernel polling to request that the netisr thread be
   * scheduled even if no packets are pending for protocols.
   */
  void
  netisr_sched_poll(void)
  {
          struct netisr_workstream *nwsp;
  
          nwsp = DPCPU_ID_PTR(nws_array[0], nws);
          NWS_SIGNAL(nwsp);
  }
  #endif
  
  static void
  netisr_start_swi(u_int cpuid, struct pcpu *pc)
  {
          char swiname[12];
          struct netisr_workstream *nwsp;
          int error;
  
          KASSERT(!CPU_ABSENT(cpuid), ("%s: CPU %u absent", __func__, cpuid));
  
          nwsp = DPCPU_ID_PTR(cpuid, nws);
          mtx_init(&nwsp->nws_mtx, "netisr_mtx", NULL, MTX_DEF);
          nwsp->nws_cpu = cpuid;
          snprintf(swiname, sizeof(swiname), "netisr %u", cpuid);
          error = swi_add(&nwsp->nws_intr_event, swiname, swi_net, nwsp,
              SWI_NET, INTR_TYPE_NET | INTR_MPSAFE, &nwsp->nws_swi_cookie);
          if (error)
                  panic("%s: swi_add %d", __func__, error);
          pc->pc_netisr = nwsp->nws_intr_event;
          if (netisr_bindthreads) {
                  error = intr_event_bind(nwsp->nws_intr_event, cpuid);
                  if (error != 0)
                          printf("%s: cpu %u: intr_event_bind: %d", __func__,
                              cpuid, error);
          }
          NETISR_WLOCK();
          nws_array[nws_count] = nwsp->nws_cpu;
          nws_count++;
          NETISR_WUNLOCK();
  }
  
  /*
   * Initialize the netisr subsystem.  We rely on BSS and static initialization
   * of most fields in global data structures.
   *
   * Start a worker thread for the boot CPU so that we can support network
   * traffic immediately in case the network stack is used before additional
   * CPUs are started (for example, diskless boot).
   */
  static void
  netisr_init(void *arg)
  {
          struct pcpu *pc;
  
          NETISR_LOCK_INIT();
          if (netisr_maxthreads == 0 || netisr_maxthreads < -1 )
                  netisr_maxthreads = 1;          /* default behavior */
          else if (netisr_maxthreads == -1)
                  netisr_maxthreads = mp_ncpus;   /* use max cpus */
          if (netisr_maxthreads > mp_ncpus) {
                  printf("netisr_init: forcing maxthreads from %d to %d\n",
                      netisr_maxthreads, mp_ncpus);
                  netisr_maxthreads = mp_ncpus;
          }
          if (netisr_defaultqlimit > netisr_maxqlimit) {
                  printf("netisr_init: forcing defaultqlimit from %d to %d\n",
                      netisr_defaultqlimit, netisr_maxqlimit);
                  netisr_defaultqlimit = netisr_maxqlimit;
          }
  #ifdef DEVICE_POLLING
          /*
           * The device polling code is not yet aware of how to deal with
           * multiple netisr threads, so for the time being compiling in device
           * polling disables parallel netisr workers.
           */
          if (netisr_maxthreads != 1 || netisr_bindthreads != 0) {
                  printf("netisr_init: forcing maxthreads to 1 and "
                      "bindthreads to 0 for device polling\n");
                  netisr_maxthreads = 1;
                  netisr_bindthreads = 0;
          }
  #endif
  
  #ifdef EARLY_AP_STARTUP
          STAILQ_FOREACH(pc, &cpuhead, pc_allcpu) {
                  if (nws_count >= netisr_maxthreads)
                          break;
                  netisr_start_swi(pc->pc_cpuid, pc);
          }
  #else
          pc = get_pcpu();
          netisr_start_swi(pc->pc_cpuid, pc);
  #endif
  }
  SYSINIT(netisr_init, SI_SUB_SOFTINTR, SI_ORDER_FIRST, netisr_init, NULL);
  
  #ifndef EARLY_AP_STARTUP
  /*
   * Start worker threads for additional CPUs.  No attempt to gracefully handle
   * work reassignment, we don't yet support dynamic reconfiguration.
   */
  static void
  netisr_start(void *arg)
  {
          struct pcpu *pc;
  
          STAILQ_FOREACH(pc, &cpuhead, pc_allcpu) {
                  if (nws_count >= netisr_maxthreads)
                          break;
                  /* Worker will already be present for boot CPU. */
                  if (pc->pc_netisr != NULL)
                          continue;
                  netisr_start_swi(pc->pc_cpuid, pc);
          }
  }
  SYSINIT(netisr_start, SI_SUB_SMP, SI_ORDER_MIDDLE, netisr_start, NULL);
  #endif
  
  /*
   * Sysctl monitoring for netisr: query a list of registered protocols.
   */
  static int
  sysctl_netisr_proto(SYSCTL_HANDLER_ARGS)
  {
          struct rm_priotracker tracker;
          struct sysctl_netisr_proto *snpp, *snp_array;
          struct netisr_proto *npp;
          u_int counter, proto;
          int error;
  
          if (req->newptr != NULL)
                  return (EINVAL);
          snp_array = malloc(sizeof(*snp_array) * NETISR_MAXPROT, M_TEMP,
              M_ZERO | M_WAITOK);
          counter = 0;
          NETISR_RLOCK(&tracker);
          for (proto = 0; proto < NETISR_MAXPROT; proto++) {
                  npp = &netisr_proto[proto];
                  if (npp->np_name == NULL)
                          continue;
                  snpp = &snp_array[counter];
                  snpp->snp_version = sizeof(*snpp);
                  strlcpy(snpp->snp_name, npp->np_name, NETISR_NAMEMAXLEN);
                  snpp->snp_proto = proto;
                  snpp->snp_qlimit = npp->np_qlimit;
                  snpp->snp_policy = npp->np_policy;
                  snpp->snp_dispatch = npp->np_dispatch;
                  if (npp->np_m2flow != NULL)
                          snpp->snp_flags |= NETISR_SNP_FLAGS_M2FLOW;
                  if (npp->np_m2cpuid != NULL)
                          snpp->snp_flags |= NETISR_SNP_FLAGS_M2CPUID;
                  if (npp->np_drainedcpu != NULL)
                          snpp->snp_flags |= NETISR_SNP_FLAGS_DRAINEDCPU;
                  counter++;
          }
          NETISR_RUNLOCK(&tracker);
          KASSERT(counter <= NETISR_MAXPROT,
              ("sysctl_netisr_proto: counter too big (%d)", counter));
          error = SYSCTL_OUT(req, snp_array, sizeof(*snp_array) * counter);
          free(snp_array, M_TEMP);
          return (error);
  }
  
  SYSCTL_PROC(_net_isr, OID_AUTO, proto,
      CTLFLAG_RD|CTLTYPE_STRUCT|CTLFLAG_MPSAFE, 0, 0, sysctl_netisr_proto,
      "S,sysctl_netisr_proto",
      "Return list of protocols registered with netisr");
  
  /*
   * Sysctl monitoring for netisr: query a list of workstreams.
   */
  static int
  sysctl_netisr_workstream(SYSCTL_HANDLER_ARGS)
  {
          struct rm_priotracker tracker;
          struct sysctl_netisr_workstream *snwsp, *snws_array;
          struct netisr_workstream *nwsp;
          u_int counter, cpuid;
          int error;
  
          if (req->newptr != NULL)
                  return (EINVAL);
          snws_array = malloc(sizeof(*snws_array) * MAXCPU, M_TEMP,
              M_ZERO | M_WAITOK);
          counter = 0;
          NETISR_RLOCK(&tracker);
          CPU_FOREACH(cpuid) {
                  nwsp = DPCPU_ID_PTR(cpuid, nws);
                  if (nwsp->nws_intr_event == NULL)
                          continue;
                  NWS_LOCK(nwsp);
                  snwsp = &snws_array[counter];
                  snwsp->snws_version = sizeof(*snwsp);
  
                  /*
                   * For now, we equate workstream IDs and CPU IDs in the
                   * kernel, but expose them independently to userspace in case
                   * that assumption changes in the future.
                   */
                  snwsp->snws_wsid = cpuid;
                  snwsp->snws_cpu = cpuid;
                  if (nwsp->nws_intr_event != NULL)
                          snwsp->snws_flags |= NETISR_SNWS_FLAGS_INTR;
                  NWS_UNLOCK(nwsp);
                  counter++;
          }
          NETISR_RUNLOCK(&tracker);
          KASSERT(counter <= MAXCPU,
              ("sysctl_netisr_workstream: counter too big (%d)", counter));
          error = SYSCTL_OUT(req, snws_array, sizeof(*snws_array) * counter);
          free(snws_array, M_TEMP);
          return (error);
  }
  
  SYSCTL_PROC(_net_isr, OID_AUTO, workstream,
      CTLFLAG_RD|CTLTYPE_STRUCT|CTLFLAG_MPSAFE, 0, 0, sysctl_netisr_workstream,
      "S,sysctl_netisr_workstream",
      "Return list of workstreams implemented by netisr");
  
  /*
   * Sysctl monitoring for netisr: query per-protocol data across all
   * workstreams.
   */
  static int
  sysctl_netisr_work(SYSCTL_HANDLER_ARGS)
  {
          struct rm_priotracker tracker;
          struct sysctl_netisr_work *snwp, *snw_array;
          struct netisr_workstream *nwsp;
          struct netisr_proto *npp;
          struct netisr_work *nwp;
          u_int counter, cpuid, proto;
          int error;
  
          if (req->newptr != NULL)
                  return (EINVAL);
          snw_array = malloc(sizeof(*snw_array) * MAXCPU * NETISR_MAXPROT,
              M_TEMP, M_ZERO | M_WAITOK);
          counter = 0;
          NETISR_RLOCK(&tracker);
          CPU_FOREACH(cpuid) {
                  nwsp = DPCPU_ID_PTR(cpuid, nws);
                  if (nwsp->nws_intr_event == NULL)
                          continue;
                  NWS_LOCK(nwsp);
                  for (proto = 0; proto < NETISR_MAXPROT; proto++) {
                          npp = &netisr_proto[proto];
                          if (npp->np_name == NULL)
                                  continue;
                          nwp = &nwsp->nws_work[proto];
                          snwp = &snw_array[counter];
                          snwp->snw_version = sizeof(*snwp);
                          snwp->snw_wsid = cpuid;         /* See comment above. */
                          snwp->snw_proto = proto;
                          snwp->snw_len = nwp->nw_len;
                          snwp->snw_watermark = nwp->nw_watermark;
                          snwp->snw_dispatched = nwp->nw_dispatched;
                          snwp->snw_hybrid_dispatched =
                              nwp->nw_hybrid_dispatched;
                          snwp->snw_qdrops = nwp->nw_qdrops;
                          snwp->snw_queued = nwp->nw_queued;
                          snwp->snw_handled = nwp->nw_handled;
                          counter++;
                  }
                  NWS_UNLOCK(nwsp);
          }
          KASSERT(counter <= MAXCPU * NETISR_MAXPROT,
              ("sysctl_netisr_work: counter too big (%d)", counter));
          NETISR_RUNLOCK(&tracker);
          error = SYSCTL_OUT(req, snw_array, sizeof(*snw_array) * counter);
          free(snw_array, M_TEMP);
          return (error);
  }
  
  SYSCTL_PROC(_net_isr, OID_AUTO, work,
      CTLFLAG_RD|CTLTYPE_STRUCT|CTLFLAG_MPSAFE, 0, 0, sysctl_netisr_work,
      "S,sysctl_netisr_work",
      "Return list of per-workstream, per-protocol work in netisr");
  
  #ifdef DDB
  DB_SHOW_COMMAND(netisr, db_show_netisr)
  {
          struct netisr_workstream *nwsp;
          struct netisr_work *nwp;
          int first, proto;
          u_int cpuid;
  
          db_printf("%3s %6s %5s %5s %5s %8s %8s %8s %8s\n", "CPU", "Proto",
              "Len", "WMark", "Max", "Disp", "HDisp", "Drop", "Queue");
          CPU_FOREACH(cpuid) {
                  nwsp = DPCPU_ID_PTR(cpuid, nws);
                  if (nwsp->nws_intr_event == NULL)
                          continue;
                  first = 1;
                  for (proto = 0; proto < NETISR_MAXPROT; proto++) {
                          if (netisr_proto[proto].np_handler == NULL)
                                  continue;
                          nwp = &nwsp->nws_work[proto];
                          if (first) {
                                  db_printf("%3d ", cpuid);
                                  first = 0;
                          } else
                                  db_printf("%3s ", "");
                          db_printf(
                              "%6s %5d %5d %5d %8ju %8ju %8ju %8ju\n",
                              netisr_proto[proto].np_name, nwp->nw_len,
                              nwp->nw_watermark, nwp->nw_qlimit,
                              nwp->nw_dispatched, nwp->nw_hybrid_dispatched,
                              nwp->nw_qdrops, nwp->nw_queued);
                  }
          }
  }
  #endif

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