FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_poll.c
1 /*-
2 * Copyright (c) 2001-2002 Luigi Rizzo
3 *
4 * Supported by: the Xorp Project (www.xorp.org)
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #include <sys/cdefs.h>
29 __FBSDID("$FreeBSD: releng/9.0/sys/kern/kern_poll.c 196267 2009-08-15 23:07:43Z rwatson $");
30
31 #include "opt_device_polling.h"
32
33 #include <sys/param.h>
34 #include <sys/systm.h>
35 #include <sys/kernel.h>
36 #include <sys/kthread.h>
37 #include <sys/proc.h>
38 #include <sys/eventhandler.h>
39 #include <sys/resourcevar.h>
40 #include <sys/socket.h> /* needed by net/if.h */
41 #include <sys/sockio.h>
42 #include <sys/sysctl.h>
43 #include <sys/syslog.h>
44
45 #include <net/if.h> /* for IFF_* flags */
46 #include <net/netisr.h> /* for NETISR_POLL */
47 #include <net/vnet.h>
48
49 void hardclock_device_poll(void); /* hook from hardclock */
50
51 static struct mtx poll_mtx;
52
53 /*
54 * Polling support for [network] device drivers.
55 *
56 * Drivers which support this feature can register with the
57 * polling code.
58 *
59 * If registration is successful, the driver must disable interrupts,
60 * and further I/O is performed through the handler, which is invoked
61 * (at least once per clock tick) with 3 arguments: the "arg" passed at
62 * register time (a struct ifnet pointer), a command, and a "count" limit.
63 *
64 * The command can be one of the following:
65 * POLL_ONLY: quick move of "count" packets from input/output queues.
66 * POLL_AND_CHECK_STATUS: as above, plus check status registers or do
67 * other more expensive operations. This command is issued periodically
68 * but less frequently than POLL_ONLY.
69 *
70 * The count limit specifies how much work the handler can do during the
71 * call -- typically this is the number of packets to be received, or
72 * transmitted, etc. (drivers are free to interpret this number, as long
73 * as the max time spent in the function grows roughly linearly with the
74 * count).
75 *
76 * Polling is enabled and disabled via setting IFCAP_POLLING flag on
77 * the interface. The driver ioctl handler should register interface
78 * with polling and disable interrupts, if registration was successful.
79 *
80 * A second variable controls the sharing of CPU between polling/kernel
81 * network processing, and other activities (typically userlevel tasks):
82 * kern.polling.user_frac (between 0 and 100, default 50) sets the share
83 * of CPU allocated to user tasks. CPU is allocated proportionally to the
84 * shares, by dynamically adjusting the "count" (poll_burst).
85 *
86 * Other parameters can should be left to their default values.
87 * The following constraints hold
88 *
89 * 1 <= poll_each_burst <= poll_burst <= poll_burst_max
90 * 0 <= poll_each_burst
91 * MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
92 */
93
94 #define MIN_POLL_BURST_MAX 10
95 #define MAX_POLL_BURST_MAX 1000
96
97 static uint32_t poll_burst = 5;
98 static uint32_t poll_burst_max = 150; /* good for 100Mbit net and HZ=1000 */
99 static uint32_t poll_each_burst = 5;
100
101 SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
102 "Device polling parameters");
103
104 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
105 &poll_burst, 0, "Current polling burst size");
106
107 static int netisr_poll_scheduled;
108 static int netisr_pollmore_scheduled;
109 static int poll_shutting_down;
110
111 static int poll_burst_max_sysctl(SYSCTL_HANDLER_ARGS)
112 {
113 uint32_t val = poll_burst_max;
114 int error;
115
116 error = sysctl_handle_int(oidp, &val, 0, req);
117 if (error || !req->newptr )
118 return (error);
119 if (val < MIN_POLL_BURST_MAX || val > MAX_POLL_BURST_MAX)
120 return (EINVAL);
121
122 mtx_lock(&poll_mtx);
123 poll_burst_max = val;
124 if (poll_burst > poll_burst_max)
125 poll_burst = poll_burst_max;
126 if (poll_each_burst > poll_burst_max)
127 poll_each_burst = MIN_POLL_BURST_MAX;
128 mtx_unlock(&poll_mtx);
129
130 return (0);
131 }
132 SYSCTL_PROC(_kern_polling, OID_AUTO, burst_max, CTLTYPE_UINT | CTLFLAG_RW,
133 0, sizeof(uint32_t), poll_burst_max_sysctl, "I", "Max Polling burst size");
134
135 static int poll_each_burst_sysctl(SYSCTL_HANDLER_ARGS)
136 {
137 uint32_t val = poll_each_burst;
138 int error;
139
140 error = sysctl_handle_int(oidp, &val, 0, req);
141 if (error || !req->newptr )
142 return (error);
143 if (val < 1)
144 return (EINVAL);
145
146 mtx_lock(&poll_mtx);
147 if (val > poll_burst_max) {
148 mtx_unlock(&poll_mtx);
149 return (EINVAL);
150 }
151 poll_each_burst = val;
152 mtx_unlock(&poll_mtx);
153
154 return (0);
155 }
156 SYSCTL_PROC(_kern_polling, OID_AUTO, each_burst, CTLTYPE_UINT | CTLFLAG_RW,
157 0, sizeof(uint32_t), poll_each_burst_sysctl, "I",
158 "Max size of each burst");
159
160 static uint32_t poll_in_idle_loop=0; /* do we poll in idle loop ? */
161 SYSCTL_UINT(_kern_polling, OID_AUTO, idle_poll, CTLFLAG_RW,
162 &poll_in_idle_loop, 0, "Enable device polling in idle loop");
163
164 static uint32_t user_frac = 50;
165 static int user_frac_sysctl(SYSCTL_HANDLER_ARGS)
166 {
167 uint32_t val = user_frac;
168 int error;
169
170 error = sysctl_handle_int(oidp, &val, 0, req);
171 if (error || !req->newptr )
172 return (error);
173 if (val < 0 || val > 99)
174 return (EINVAL);
175
176 mtx_lock(&poll_mtx);
177 user_frac = val;
178 mtx_unlock(&poll_mtx);
179
180 return (0);
181 }
182 SYSCTL_PROC(_kern_polling, OID_AUTO, user_frac, CTLTYPE_UINT | CTLFLAG_RW,
183 0, sizeof(uint32_t), user_frac_sysctl, "I",
184 "Desired user fraction of cpu time");
185
186 static uint32_t reg_frac_count = 0;
187 static uint32_t reg_frac = 20 ;
188 static int reg_frac_sysctl(SYSCTL_HANDLER_ARGS)
189 {
190 uint32_t val = reg_frac;
191 int error;
192
193 error = sysctl_handle_int(oidp, &val, 0, req);
194 if (error || !req->newptr )
195 return (error);
196 if (val < 1 || val > hz)
197 return (EINVAL);
198
199 mtx_lock(&poll_mtx);
200 reg_frac = val;
201 if (reg_frac_count >= reg_frac)
202 reg_frac_count = 0;
203 mtx_unlock(&poll_mtx);
204
205 return (0);
206 }
207 SYSCTL_PROC(_kern_polling, OID_AUTO, reg_frac, CTLTYPE_UINT | CTLFLAG_RW,
208 0, sizeof(uint32_t), reg_frac_sysctl, "I",
209 "Every this many cycles check registers");
210
211 static uint32_t short_ticks;
212 SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RD,
213 &short_ticks, 0, "Hardclock ticks shorter than they should be");
214
215 static uint32_t lost_polls;
216 SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RD,
217 &lost_polls, 0, "How many times we would have lost a poll tick");
218
219 static uint32_t pending_polls;
220 SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RD,
221 &pending_polls, 0, "Do we need to poll again");
222
223 static int residual_burst = 0;
224 SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RD,
225 &residual_burst, 0, "# of residual cycles in burst");
226
227 static uint32_t poll_handlers; /* next free entry in pr[]. */
228 SYSCTL_UINT(_kern_polling, OID_AUTO, handlers, CTLFLAG_RD,
229 &poll_handlers, 0, "Number of registered poll handlers");
230
231 static uint32_t phase;
232 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
233 &phase, 0, "Polling phase");
234
235 static uint32_t suspect;
236 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
237 &suspect, 0, "suspect event");
238
239 static uint32_t stalled;
240 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
241 &stalled, 0, "potential stalls");
242
243 static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
244 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
245 &idlepoll_sleeping, 0, "idlepoll is sleeping");
246
247
248 #define POLL_LIST_LEN 128
249 struct pollrec {
250 poll_handler_t *handler;
251 struct ifnet *ifp;
252 };
253
254 static struct pollrec pr[POLL_LIST_LEN];
255
256 static void
257 poll_shutdown(void *arg, int howto)
258 {
259
260 poll_shutting_down = 1;
261 }
262
263 static void
264 init_device_poll(void)
265 {
266
267 mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
268 EVENTHANDLER_REGISTER(shutdown_post_sync, poll_shutdown, NULL,
269 SHUTDOWN_PRI_LAST);
270 }
271 SYSINIT(device_poll, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, init_device_poll, NULL);
272
273
274 /*
275 * Hook from hardclock. Tries to schedule a netisr, but keeps track
276 * of lost ticks due to the previous handler taking too long.
277 * Normally, this should not happen, because polling handler should
278 * run for a short time. However, in some cases (e.g. when there are
279 * changes in link status etc.) the drivers take a very long time
280 * (even in the order of milliseconds) to reset and reconfigure the
281 * device, causing apparent lost polls.
282 *
283 * The first part of the code is just for debugging purposes, and tries
284 * to count how often hardclock ticks are shorter than they should,
285 * meaning either stray interrupts or delayed events.
286 */
287 void
288 hardclock_device_poll(void)
289 {
290 static struct timeval prev_t, t;
291 int delta;
292
293 if (poll_handlers == 0 || poll_shutting_down)
294 return;
295
296 microuptime(&t);
297 delta = (t.tv_usec - prev_t.tv_usec) +
298 (t.tv_sec - prev_t.tv_sec)*1000000;
299 if (delta * hz < 500000)
300 short_ticks++;
301 else
302 prev_t = t;
303
304 if (pending_polls > 100) {
305 /*
306 * Too much, assume it has stalled (not always true
307 * see comment above).
308 */
309 stalled++;
310 pending_polls = 0;
311 phase = 0;
312 }
313
314 if (phase <= 2) {
315 if (phase != 0)
316 suspect++;
317 phase = 1;
318 netisr_poll_scheduled = 1;
319 netisr_pollmore_scheduled = 1;
320 netisr_sched_poll();
321 phase = 2;
322 }
323 if (pending_polls++ > 0)
324 lost_polls++;
325 }
326
327 /*
328 * ether_poll is called from the idle loop.
329 */
330 static void
331 ether_poll(int count)
332 {
333 int i;
334
335 mtx_lock(&poll_mtx);
336
337 if (count > poll_each_burst)
338 count = poll_each_burst;
339
340 for (i = 0 ; i < poll_handlers ; i++)
341 pr[i].handler(pr[i].ifp, POLL_ONLY, count);
342
343 mtx_unlock(&poll_mtx);
344 }
345
346 /*
347 * netisr_pollmore is called after other netisr's, possibly scheduling
348 * another NETISR_POLL call, or adapting the burst size for the next cycle.
349 *
350 * It is very bad to fetch large bursts of packets from a single card at once,
351 * because the burst could take a long time to be completely processed, or
352 * could saturate the intermediate queue (ipintrq or similar) leading to
353 * losses or unfairness. To reduce the problem, and also to account better for
354 * time spent in network-related processing, we split the burst in smaller
355 * chunks of fixed size, giving control to the other netisr's between chunks.
356 * This helps in improving the fairness, reducing livelock (because we
357 * emulate more closely the "process to completion" that we have with
358 * fastforwarding) and accounting for the work performed in low level
359 * handling and forwarding.
360 */
361
362 static struct timeval poll_start_t;
363
364 void
365 netisr_pollmore()
366 {
367 struct timeval t;
368 int kern_load;
369
370 mtx_lock(&poll_mtx);
371 if (!netisr_pollmore_scheduled) {
372 mtx_unlock(&poll_mtx);
373 return;
374 }
375 netisr_pollmore_scheduled = 0;
376 phase = 5;
377 if (residual_burst > 0) {
378 netisr_poll_scheduled = 1;
379 netisr_pollmore_scheduled = 1;
380 netisr_sched_poll();
381 mtx_unlock(&poll_mtx);
382 /* will run immediately on return, followed by netisrs */
383 return;
384 }
385 /* here we can account time spent in netisr's in this tick */
386 microuptime(&t);
387 kern_load = (t.tv_usec - poll_start_t.tv_usec) +
388 (t.tv_sec - poll_start_t.tv_sec)*1000000; /* us */
389 kern_load = (kern_load * hz) / 10000; /* 0..100 */
390 if (kern_load > (100 - user_frac)) { /* try decrease ticks */
391 if (poll_burst > 1)
392 poll_burst--;
393 } else {
394 if (poll_burst < poll_burst_max)
395 poll_burst++;
396 }
397
398 pending_polls--;
399 if (pending_polls == 0) /* we are done */
400 phase = 0;
401 else {
402 /*
403 * Last cycle was long and caused us to miss one or more
404 * hardclock ticks. Restart processing again, but slightly
405 * reduce the burst size to prevent that this happens again.
406 */
407 poll_burst -= (poll_burst / 8);
408 if (poll_burst < 1)
409 poll_burst = 1;
410 netisr_poll_scheduled = 1;
411 netisr_pollmore_scheduled = 1;
412 netisr_sched_poll();
413 phase = 6;
414 }
415 mtx_unlock(&poll_mtx);
416 }
417
418 /*
419 * netisr_poll is typically scheduled once per tick.
420 */
421 void
422 netisr_poll(void)
423 {
424 int i, cycles;
425 enum poll_cmd arg = POLL_ONLY;
426
427 mtx_lock(&poll_mtx);
428 if (!netisr_poll_scheduled) {
429 mtx_unlock(&poll_mtx);
430 return;
431 }
432 netisr_poll_scheduled = 0;
433 phase = 3;
434 if (residual_burst == 0) { /* first call in this tick */
435 microuptime(&poll_start_t);
436 if (++reg_frac_count == reg_frac) {
437 arg = POLL_AND_CHECK_STATUS;
438 reg_frac_count = 0;
439 }
440
441 residual_burst = poll_burst;
442 }
443 cycles = (residual_burst < poll_each_burst) ?
444 residual_burst : poll_each_burst;
445 residual_burst -= cycles;
446
447 for (i = 0 ; i < poll_handlers ; i++)
448 pr[i].handler(pr[i].ifp, arg, cycles);
449
450 phase = 4;
451 mtx_unlock(&poll_mtx);
452 }
453
454 /*
455 * Try to register routine for polling. Returns 0 if successful
456 * (and polling should be enabled), error code otherwise.
457 * A device is not supposed to register itself multiple times.
458 *
459 * This is called from within the *_ioctl() functions.
460 */
461 int
462 ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
463 {
464 int i;
465
466 KASSERT(h != NULL, ("%s: handler is NULL", __func__));
467 KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
468
469 mtx_lock(&poll_mtx);
470 if (poll_handlers >= POLL_LIST_LEN) {
471 /*
472 * List full, cannot register more entries.
473 * This should never happen; if it does, it is probably a
474 * broken driver trying to register multiple times. Checking
475 * this at runtime is expensive, and won't solve the problem
476 * anyways, so just report a few times and then give up.
477 */
478 static int verbose = 10 ;
479 if (verbose >0) {
480 log(LOG_ERR, "poll handlers list full, "
481 "maybe a broken driver ?\n");
482 verbose--;
483 }
484 mtx_unlock(&poll_mtx);
485 return (ENOMEM); /* no polling for you */
486 }
487
488 for (i = 0 ; i < poll_handlers ; i++)
489 if (pr[i].ifp == ifp && pr[i].handler != NULL) {
490 mtx_unlock(&poll_mtx);
491 log(LOG_DEBUG, "ether_poll_register: %s: handler"
492 " already registered\n", ifp->if_xname);
493 return (EEXIST);
494 }
495
496 pr[poll_handlers].handler = h;
497 pr[poll_handlers].ifp = ifp;
498 poll_handlers++;
499 mtx_unlock(&poll_mtx);
500 if (idlepoll_sleeping)
501 wakeup(&idlepoll_sleeping);
502 return (0);
503 }
504
505 /*
506 * Remove interface from the polling list. Called from *_ioctl(), too.
507 */
508 int
509 ether_poll_deregister(struct ifnet *ifp)
510 {
511 int i;
512
513 KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
514
515 mtx_lock(&poll_mtx);
516
517 for (i = 0 ; i < poll_handlers ; i++)
518 if (pr[i].ifp == ifp) /* found it */
519 break;
520 if (i == poll_handlers) {
521 log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
522 ifp->if_xname);
523 mtx_unlock(&poll_mtx);
524 return (ENOENT);
525 }
526 poll_handlers--;
527 if (i < poll_handlers) { /* Last entry replaces this one. */
528 pr[i].handler = pr[poll_handlers].handler;
529 pr[i].ifp = pr[poll_handlers].ifp;
530 }
531 mtx_unlock(&poll_mtx);
532 return (0);
533 }
534
535 static void
536 poll_idle(void)
537 {
538 struct thread *td = curthread;
539 struct rtprio rtp;
540
541 rtp.prio = RTP_PRIO_MAX; /* lowest priority */
542 rtp.type = RTP_PRIO_IDLE;
543 PROC_SLOCK(td->td_proc);
544 rtp_to_pri(&rtp, td);
545 PROC_SUNLOCK(td->td_proc);
546
547 for (;;) {
548 if (poll_in_idle_loop && poll_handlers > 0) {
549 idlepoll_sleeping = 0;
550 ether_poll(poll_each_burst);
551 thread_lock(td);
552 mi_switch(SW_VOL, NULL);
553 thread_unlock(td);
554 } else {
555 idlepoll_sleeping = 1;
556 tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
557 }
558 }
559 }
560
561 static struct proc *idlepoll;
562 static struct kproc_desc idlepoll_kp = {
563 "idlepoll",
564 poll_idle,
565 &idlepoll
566 };
567 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
568 &idlepoll_kp);
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