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/7.4/sys/kern/kern_poll.c 180695 2008-07-22 14:27:47Z 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/socket.h> /* needed by net/if.h */
37 #include <sys/sockio.h>
38 #include <sys/sysctl.h>
39 #include <sys/syslog.h>
40
41 #include <net/if.h> /* for IFF_* flags */
42 #include <net/netisr.h> /* for NETISR_POLL */
43
44 #include <sys/proc.h>
45 #include <sys/resourcevar.h>
46 #include <sys/kthread.h>
47
48 static void netisr_poll(void); /* the two netisr handlers */
49 static void netisr_pollmore(void);
50 static int poll_switch(SYSCTL_HANDLER_ARGS);
51
52 void hardclock_device_poll(void); /* hook from hardclock */
53 void ether_poll(int); /* polling in idle loop */
54
55 static struct mtx poll_mtx;
56
57 /*
58 * Polling support for [network] device drivers.
59 *
60 * Drivers which support this feature can register with the
61 * polling code.
62 *
63 * If registration is successful, the driver must disable interrupts,
64 * and further I/O is performed through the handler, which is invoked
65 * (at least once per clock tick) with 3 arguments: the "arg" passed at
66 * register time (a struct ifnet pointer), a command, and a "count" limit.
67 *
68 * The command can be one of the following:
69 * POLL_ONLY: quick move of "count" packets from input/output queues.
70 * POLL_AND_CHECK_STATUS: as above, plus check status registers or do
71 * other more expensive operations. This command is issued periodically
72 * but less frequently than POLL_ONLY.
73 *
74 * The count limit specifies how much work the handler can do during the
75 * call -- typically this is the number of packets to be received, or
76 * transmitted, etc. (drivers are free to interpret this number, as long
77 * as the max time spent in the function grows roughly linearly with the
78 * count).
79 *
80 * Polling is enabled and disabled via setting IFCAP_POLLING flag on
81 * the interface. The driver ioctl handler should register interface
82 * with polling and disable interrupts, if registration was successful.
83 *
84 * A second variable controls the sharing of CPU between polling/kernel
85 * network processing, and other activities (typically userlevel tasks):
86 * kern.polling.user_frac (between 0 and 100, default 50) sets the share
87 * of CPU allocated to user tasks. CPU is allocated proportionally to the
88 * shares, by dynamically adjusting the "count" (poll_burst).
89 *
90 * Other parameters can should be left to their default values.
91 * The following constraints hold
92 *
93 * 1 <= poll_each_burst <= poll_burst <= poll_burst_max
94 * 0 <= poll_each_burst
95 * MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
96 */
97
98 #define MIN_POLL_BURST_MAX 10
99 #define MAX_POLL_BURST_MAX 1000
100
101 static uint32_t poll_burst = 5;
102 static uint32_t poll_burst_max = 150; /* good for 100Mbit net and HZ=1000 */
103 static uint32_t poll_each_burst = 5;
104
105 SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
106 "Device polling parameters");
107
108 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RD,
109 &poll_burst, 0, "Current polling burst size");
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 int polling = 0;
232 SYSCTL_PROC(_kern_polling, OID_AUTO, enable, CTLTYPE_UINT | CTLFLAG_RW,
233 0, sizeof(int), poll_switch, "I", "Switch polling for all interfaces");
234
235 static uint32_t phase;
236 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RD,
237 &phase, 0, "Polling phase");
238
239 static uint32_t suspect;
240 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RD,
241 &suspect, 0, "suspect event");
242
243 static uint32_t stalled;
244 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RD,
245 &stalled, 0, "potential stalls");
246
247 static uint32_t idlepoll_sleeping; /* idlepoll is sleeping */
248 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
249 &idlepoll_sleeping, 0, "idlepoll is sleeping");
250
251
252 #define POLL_LIST_LEN 128
253 struct pollrec {
254 poll_handler_t *handler;
255 struct ifnet *ifp;
256 };
257
258 static struct pollrec pr[POLL_LIST_LEN];
259
260 static void
261 init_device_poll(void)
262 {
263
264 mtx_init(&poll_mtx, "polling", NULL, MTX_DEF);
265 netisr_register(NETISR_POLL, (netisr_t *)netisr_poll, NULL,
266 NETISR_MPSAFE);
267 netisr_register(NETISR_POLLMORE, (netisr_t *)netisr_pollmore, NULL,
268 NETISR_MPSAFE);
269 }
270 SYSINIT(device_poll, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, init_device_poll, NULL);
271
272
273 /*
274 * Hook from hardclock. Tries to schedule a netisr, but keeps track
275 * of lost ticks due to the previous handler taking too long.
276 * Normally, this should not happen, because polling handler should
277 * run for a short time. However, in some cases (e.g. when there are
278 * changes in link status etc.) the drivers take a very long time
279 * (even in the order of milliseconds) to reset and reconfigure the
280 * device, causing apparent lost polls.
281 *
282 * The first part of the code is just for debugging purposes, and tries
283 * to count how often hardclock ticks are shorter than they should,
284 * meaning either stray interrupts or delayed events.
285 */
286 void
287 hardclock_device_poll(void)
288 {
289 static struct timeval prev_t, t;
290 int delta;
291
292 if (poll_handlers == 0)
293 return;
294
295 microuptime(&t);
296 delta = (t.tv_usec - prev_t.tv_usec) +
297 (t.tv_sec - prev_t.tv_sec)*1000000;
298 if (delta * hz < 500000)
299 short_ticks++;
300 else
301 prev_t = t;
302
303 if (pending_polls > 100) {
304 /*
305 * Too much, assume it has stalled (not always true
306 * see comment above).
307 */
308 stalled++;
309 pending_polls = 0;
310 phase = 0;
311 }
312
313 if (phase <= 2) {
314 if (phase != 0)
315 suspect++;
316 phase = 1;
317 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
318 phase = 2;
319 }
320 if (pending_polls++ > 0)
321 lost_polls++;
322 }
323
324 /*
325 * ether_poll is called from the idle loop.
326 */
327 void
328 ether_poll(int count)
329 {
330 int i;
331
332 mtx_lock(&poll_mtx);
333
334 if (count > poll_each_burst)
335 count = poll_each_burst;
336
337 for (i = 0 ; i < poll_handlers ; i++)
338 pr[i].handler(pr[i].ifp, POLL_ONLY, count);
339
340 mtx_unlock(&poll_mtx);
341 }
342
343 /*
344 * netisr_pollmore is called after other netisr's, possibly scheduling
345 * another NETISR_POLL call, or adapting the burst size for the next cycle.
346 *
347 * It is very bad to fetch large bursts of packets from a single card at once,
348 * because the burst could take a long time to be completely processed, or
349 * could saturate the intermediate queue (ipintrq or similar) leading to
350 * losses or unfairness. To reduce the problem, and also to account better for
351 * time spent in network-related processing, we split the burst in smaller
352 * chunks of fixed size, giving control to the other netisr's between chunks.
353 * This helps in improving the fairness, reducing livelock (because we
354 * emulate more closely the "process to completion" that we have with
355 * fastforwarding) and accounting for the work performed in low level
356 * handling and forwarding.
357 */
358
359 static struct timeval poll_start_t;
360
361 void
362 netisr_pollmore()
363 {
364 struct timeval t;
365 int kern_load;
366
367 mtx_lock(&poll_mtx);
368 phase = 5;
369 if (residual_burst > 0) {
370 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
371 mtx_unlock(&poll_mtx);
372 /* will run immediately on return, followed by netisrs */
373 return;
374 }
375 /* here we can account time spent in netisr's in this tick */
376 microuptime(&t);
377 kern_load = (t.tv_usec - poll_start_t.tv_usec) +
378 (t.tv_sec - poll_start_t.tv_sec)*1000000; /* us */
379 kern_load = (kern_load * hz) / 10000; /* 0..100 */
380 if (kern_load > (100 - user_frac)) { /* try decrease ticks */
381 if (poll_burst > 1)
382 poll_burst--;
383 } else {
384 if (poll_burst < poll_burst_max)
385 poll_burst++;
386 }
387
388 pending_polls--;
389 if (pending_polls == 0) /* we are done */
390 phase = 0;
391 else {
392 /*
393 * Last cycle was long and caused us to miss one or more
394 * hardclock ticks. Restart processing again, but slightly
395 * reduce the burst size to prevent that this happens again.
396 */
397 poll_burst -= (poll_burst / 8);
398 if (poll_burst < 1)
399 poll_burst = 1;
400 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
401 phase = 6;
402 }
403 mtx_unlock(&poll_mtx);
404 }
405
406 /*
407 * netisr_poll is scheduled by schednetisr when appropriate, typically once
408 * per tick.
409 */
410 static void
411 netisr_poll(void)
412 {
413 int i, cycles;
414 enum poll_cmd arg = POLL_ONLY;
415
416 mtx_lock(&poll_mtx);
417 phase = 3;
418 if (residual_burst == 0) { /* first call in this tick */
419 microuptime(&poll_start_t);
420 if (++reg_frac_count == reg_frac) {
421 arg = POLL_AND_CHECK_STATUS;
422 reg_frac_count = 0;
423 }
424
425 residual_burst = poll_burst;
426 }
427 cycles = (residual_burst < poll_each_burst) ?
428 residual_burst : poll_each_burst;
429 residual_burst -= cycles;
430
431 for (i = 0 ; i < poll_handlers ; i++)
432 pr[i].handler(pr[i].ifp, arg, cycles);
433
434 phase = 4;
435 mtx_unlock(&poll_mtx);
436 }
437
438 /*
439 * Try to register routine for polling. Returns 0 if successful
440 * (and polling should be enabled), error code otherwise.
441 * A device is not supposed to register itself multiple times.
442 *
443 * This is called from within the *_ioctl() functions.
444 */
445 int
446 ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
447 {
448 int i;
449
450 KASSERT(h != NULL, ("%s: handler is NULL", __func__));
451 KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
452
453 mtx_lock(&poll_mtx);
454 if (poll_handlers >= POLL_LIST_LEN) {
455 /*
456 * List full, cannot register more entries.
457 * This should never happen; if it does, it is probably a
458 * broken driver trying to register multiple times. Checking
459 * this at runtime is expensive, and won't solve the problem
460 * anyways, so just report a few times and then give up.
461 */
462 static int verbose = 10 ;
463 if (verbose >0) {
464 log(LOG_ERR, "poll handlers list full, "
465 "maybe a broken driver ?\n");
466 verbose--;
467 }
468 mtx_unlock(&poll_mtx);
469 return (ENOMEM); /* no polling for you */
470 }
471
472 for (i = 0 ; i < poll_handlers ; i++)
473 if (pr[i].ifp == ifp && pr[i].handler != NULL) {
474 mtx_unlock(&poll_mtx);
475 log(LOG_DEBUG, "ether_poll_register: %s: handler"
476 " already registered\n", ifp->if_xname);
477 return (EEXIST);
478 }
479
480 pr[poll_handlers].handler = h;
481 pr[poll_handlers].ifp = ifp;
482 poll_handlers++;
483 mtx_unlock(&poll_mtx);
484 if (idlepoll_sleeping)
485 wakeup(&idlepoll_sleeping);
486 return (0);
487 }
488
489 /*
490 * Remove interface from the polling list. Called from *_ioctl(), too.
491 */
492 int
493 ether_poll_deregister(struct ifnet *ifp)
494 {
495 int i;
496
497 KASSERT(ifp != NULL, ("%s: ifp is NULL", __func__));
498
499 mtx_lock(&poll_mtx);
500
501 for (i = 0 ; i < poll_handlers ; i++)
502 if (pr[i].ifp == ifp) /* found it */
503 break;
504 if (i == poll_handlers) {
505 log(LOG_DEBUG, "ether_poll_deregister: %s: not found!\n",
506 ifp->if_xname);
507 mtx_unlock(&poll_mtx);
508 return (ENOENT);
509 }
510 poll_handlers--;
511 if (i < poll_handlers) { /* Last entry replaces this one. */
512 pr[i].handler = pr[poll_handlers].handler;
513 pr[i].ifp = pr[poll_handlers].ifp;
514 }
515 mtx_unlock(&poll_mtx);
516 return (0);
517 }
518
519 /*
520 * Legacy interface for turning polling on all interfaces at one time.
521 */
522 static int
523 poll_switch(SYSCTL_HANDLER_ARGS)
524 {
525 struct ifnet *ifp;
526 int error;
527 int val = polling;
528
529 error = sysctl_handle_int(oidp, &val, 0, req);
530 if (error || !req->newptr )
531 return (error);
532
533 if (val == polling)
534 return (0);
535
536 if (val < 0 || val > 1)
537 return (EINVAL);
538
539 polling = val;
540
541 IFNET_RLOCK();
542 TAILQ_FOREACH(ifp, &ifnet, if_link) {
543 if (ifp->if_capabilities & IFCAP_POLLING) {
544 struct ifreq ifr;
545
546 if (val == 1)
547 ifr.ifr_reqcap =
548 ifp->if_capenable | IFCAP_POLLING;
549 else
550 ifr.ifr_reqcap =
551 ifp->if_capenable & ~IFCAP_POLLING;
552 IFF_LOCKGIANT(ifp); /* LOR here */
553 (void) (*ifp->if_ioctl)(ifp, SIOCSIFCAP, (caddr_t)&ifr);
554 IFF_UNLOCKGIANT(ifp);
555 }
556 }
557 IFNET_RUNLOCK();
558
559 log(LOG_ERR, "kern.polling.enable is deprecated. Use ifconfig(8)");
560
561 return (0);
562 }
563
564 static void
565 poll_idle(void)
566 {
567 struct thread *td = curthread;
568 struct rtprio rtp;
569
570 rtp.prio = RTP_PRIO_MAX; /* lowest priority */
571 rtp.type = RTP_PRIO_IDLE;
572 PROC_SLOCK(td->td_proc);
573 rtp_to_pri(&rtp, td);
574 PROC_SUNLOCK(td->td_proc);
575
576 for (;;) {
577 if (poll_in_idle_loop && poll_handlers > 0) {
578 idlepoll_sleeping = 0;
579 ether_poll(poll_each_burst);
580 thread_lock(td);
581 mi_switch(SW_VOL, NULL);
582 thread_unlock(td);
583 } else {
584 idlepoll_sleeping = 1;
585 tsleep(&idlepoll_sleeping, 0, "pollid", hz * 3);
586 }
587 }
588 }
589
590 static struct proc *idlepoll;
591 static struct kproc_desc idlepoll_kp = {
592 "idlepoll",
593 poll_idle,
594 &idlepoll
595 };
596 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start,
597 &idlepoll_kp);
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