FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/include/sys/txg_impl.h

     /*
      * CDDL HEADER START
      *
      * The contents of this file are subject to the terms of the
      * Common Development and Distribution License (the "License").
      * You may not use this file except in compliance with the License.
      *
      * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      * or https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    
    /*
     * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
     * Use is subject to license terms.
     */
    
    /*
     * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
     */
    
    #ifndef _SYS_TXG_IMPL_H
    #define _SYS_TXG_IMPL_H
    
    #include <sys/spa.h>
    #include <sys/txg.h>
    
    #ifdef  __cplusplus
    extern "C" {
    #endif
    
    /*
     * The tx_cpu structure is a per-cpu structure that is used to track
     * the number of active transaction holds (tc_count). As transactions
     * are assigned into a transaction group the appropriate tc_count is
     * incremented to indicate that there are pending changes that have yet
     * to quiesce. Consumers eventually call txg_rele_to_sync() to decrement
     * the tc_count. A transaction group is not considered quiesced until all
     * tx_cpu structures have reached a tc_count of zero.
     *
     * This structure is a per-cpu structure by design. Updates to this structure
     * are frequent and concurrent. Having a single structure would result in
     * heavy lock contention so a per-cpu design was implemented. With the fanned
     * out mutex design, consumers only need to lock the mutex associated with
     * thread's cpu.
     *
     * The tx_cpu contains two locks, the tc_lock and tc_open_lock.
     * The tc_lock is used to protect all members of the tx_cpu structure with
     * the exception of the tc_open_lock. This lock should only be held for a
     * short period of time, typically when updating the value of tc_count.
     *
     * The tc_open_lock protects the tx_open_txg member of the tx_state structure.
     * This lock is used to ensure that transactions are only assigned into
     * the current open transaction group. In order to move the current open
     * transaction group to the quiesce phase, the txg_quiesce thread must
     * grab all tc_open_locks, increment the tx_open_txg, and drop the locks.
     * The tc_open_lock is held until the transaction is assigned into the
     * transaction group. Typically, this is a short operation but if throttling
     * is occurring it may be held for longer periods of time.
     */
    struct tx_cpu {
            kmutex_t        tc_open_lock;   /* protects tx_open_txg */
            kmutex_t        tc_lock;        /* protects the rest of this struct */
            kcondvar_t      tc_cv[TXG_SIZE];
            uint64_t        tc_count[TXG_SIZE];     /* tx hold count on each txg */
            list_t          tc_callbacks[TXG_SIZE]; /* commit cb list */
            char            tc_pad[8];              /* pad to fill 3 cache lines */
    };
    
    /*
     * The tx_state structure maintains the state information about the different
     * stages of the pool's transaction groups. A per pool tx_state structure
     * is used to track this information. The tx_state structure also points to
     * an array of tx_cpu structures (described above). Although the tx_sync_lock
     * is used to protect the members of this structure, it is not used to
     * protect the tx_open_txg. Instead a special lock in the tx_cpu structure
     * is used. Readers of tx_open_txg must grab the per-cpu tc_open_lock.
     * Any thread wishing to update tx_open_txg must grab the tc_open_lock on
     * every cpu (see txg_quiesce()).
     */
    typedef struct tx_state {
            tx_cpu_t        *tx_cpu;        /* protects access to tx_open_txg */
            kmutex_t        tx_sync_lock;   /* protects the rest of this struct */
    
            uint64_t        tx_open_txg;    /* currently open txg id */
            uint64_t        tx_quiescing_txg; /* currently quiescing txg id */
            uint64_t        tx_quiesced_txg; /* quiesced txg waiting for sync */
            uint64_t        tx_syncing_txg; /* currently syncing txg id */
            uint64_t        tx_synced_txg;  /* last synced txg id */
    
           hrtime_t        tx_open_time;   /* start time of tx_open_txg */
   
           uint64_t        tx_sync_txg_waiting; /* txg we're waiting to sync */
           uint64_t        tx_quiesce_txg_waiting; /* txg we're waiting to open */
   
           kcondvar_t      tx_sync_more_cv;
           kcondvar_t      tx_sync_done_cv;
           kcondvar_t      tx_quiesce_more_cv;
           kcondvar_t      tx_quiesce_done_cv;
           kcondvar_t      tx_timeout_cv;
           kcondvar_t      tx_exit_cv;     /* wait for all threads to exit */
   
           uint8_t         tx_threads;     /* number of threads */
           uint8_t         tx_exiting;     /* set when we're exiting */
   
           kthread_t       *tx_sync_thread;
           kthread_t       *tx_quiesce_thread;
   
           taskq_t         *tx_commit_cb_taskq; /* commit callback taskq */
   } tx_state_t;
   
   #ifdef  __cplusplus
   }
   #endif
   
   #endif  /* _SYS_TXG_IMPL_H */

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