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/5.3/sys/kern/kern_poll.c 136588 2004-10-16 08:43:07Z cvs2svn $");
30
31 #include <sys/param.h>
32 #include <sys/systm.h>
33 #include <sys/kernel.h>
34 #include <sys/socket.h> /* needed by net/if.h */
35 #include <sys/sysctl.h>
36
37 #include <net/if.h> /* for IFF_* flags */
38 #include <net/netisr.h> /* for NETISR_POLL */
39
40 #include <sys/proc.h>
41 #include <sys/resourcevar.h>
42 #include <sys/kthread.h>
43
44 #ifdef SMP
45 #ifndef COMPILING_LINT
46 #error DEVICE_POLLING is not compatible with SMP
47 #endif
48 #endif
49
50 static void netisr_poll(void); /* the two netisr handlers */
51 static void netisr_pollmore(void);
52
53 void hardclock_device_poll(void); /* hook from hardclock */
54 void ether_poll(int); /* polling while in trap */
55
56 /*
57 * Polling support for [network] device drivers.
58 *
59 * Drivers which support this feature try to register with the
60 * polling code.
61 *
62 * If registration is successful, the driver must disable interrupts,
63 * and further I/O is performed through the handler, which is invoked
64 * (at least once per clock tick) with 3 arguments: the "arg" passed at
65 * register time (a struct ifnet pointer), a command, and a "count" limit.
66 *
67 * The command can be one of the following:
68 * POLL_ONLY: quick move of "count" packets from input/output queues.
69 * POLL_AND_CHECK_STATUS: as above, plus check status registers or do
70 * other more expensive operations. This command is issued periodically
71 * but less frequently than POLL_ONLY.
72 * POLL_DEREGISTER: deregister and return to interrupt mode.
73 *
74 * The first two commands are only issued if the interface is marked as
75 * 'IFF_UP and IFF_RUNNING', the last one only if IFF_RUNNING is set.
76 *
77 * The count limit specifies how much work the handler can do during the
78 * call -- typically this is the number of packets to be received, or
79 * transmitted, etc. (drivers are free to interpret this number, as long
80 * as the max time spent in the function grows roughly linearly with the
81 * count).
82 *
83 * Deregistration can be requested by the driver itself (typically in the
84 * *_stop() routine), or by the polling code, by invoking the handler.
85 *
86 * Polling can be globally enabled or disabled with the sysctl variable
87 * kern.polling.enable (default is 0, disabled)
88 *
89 * A second variable controls the sharing of CPU between polling/kernel
90 * network processing, and other activities (typically userlevel tasks):
91 * kern.polling.user_frac (between 0 and 100, default 50) sets the share
92 * of CPU allocated to user tasks. CPU is allocated proportionally to the
93 * shares, by dynamically adjusting the "count" (poll_burst).
94 *
95 * Other parameters can should be left to their default values.
96 * The following constraints hold
97 *
98 * 1 <= poll_each_burst <= poll_burst <= poll_burst_max
99 * 0 <= poll_in_trap <= poll_each_burst
100 * MIN_POLL_BURST_MAX <= poll_burst_max <= MAX_POLL_BURST_MAX
101 */
102
103 #define MIN_POLL_BURST_MAX 10
104 #define MAX_POLL_BURST_MAX 1000
105
106 SYSCTL_NODE(_kern, OID_AUTO, polling, CTLFLAG_RW, 0,
107 "Device polling parameters");
108
109 static u_int32_t poll_burst = 5;
110 SYSCTL_UINT(_kern_polling, OID_AUTO, burst, CTLFLAG_RW,
111 &poll_burst, 0, "Current polling burst size");
112
113 static u_int32_t poll_each_burst = 5;
114 SYSCTL_UINT(_kern_polling, OID_AUTO, each_burst, CTLFLAG_RW,
115 &poll_each_burst, 0, "Max size of each burst");
116
117 static u_int32_t poll_burst_max = 150; /* good for 100Mbit net and HZ=1000 */
118 SYSCTL_UINT(_kern_polling, OID_AUTO, burst_max, CTLFLAG_RW,
119 &poll_burst_max, 0, "Max Polling burst size");
120
121 static u_int32_t poll_in_idle_loop=0; /* do we poll in idle loop ? */
122 SYSCTL_UINT(_kern_polling, OID_AUTO, idle_poll, CTLFLAG_RW,
123 &poll_in_idle_loop, 0, "Enable device polling in idle loop");
124
125 u_int32_t poll_in_trap; /* used in trap.c */
126 SYSCTL_UINT(_kern_polling, OID_AUTO, poll_in_trap, CTLFLAG_RW,
127 &poll_in_trap, 0, "Poll burst size during a trap");
128
129 static u_int32_t user_frac = 50;
130 SYSCTL_UINT(_kern_polling, OID_AUTO, user_frac, CTLFLAG_RW,
131 &user_frac, 0, "Desired user fraction of cpu time");
132
133 static u_int32_t reg_frac = 20 ;
134 SYSCTL_UINT(_kern_polling, OID_AUTO, reg_frac, CTLFLAG_RW,
135 ®_frac, 0, "Every this many cycles poll register");
136
137 static u_int32_t short_ticks;
138 SYSCTL_UINT(_kern_polling, OID_AUTO, short_ticks, CTLFLAG_RW,
139 &short_ticks, 0, "Hardclock ticks shorter than they should be");
140
141 static u_int32_t lost_polls;
142 SYSCTL_UINT(_kern_polling, OID_AUTO, lost_polls, CTLFLAG_RW,
143 &lost_polls, 0, "How many times we would have lost a poll tick");
144
145 static u_int32_t pending_polls;
146 SYSCTL_UINT(_kern_polling, OID_AUTO, pending_polls, CTLFLAG_RW,
147 &pending_polls, 0, "Do we need to poll again");
148
149 static int residual_burst = 0;
150 SYSCTL_INT(_kern_polling, OID_AUTO, residual_burst, CTLFLAG_RW,
151 &residual_burst, 0, "# of residual cycles in burst");
152
153 static u_int32_t poll_handlers; /* next free entry in pr[]. */
154 SYSCTL_UINT(_kern_polling, OID_AUTO, handlers, CTLFLAG_RD,
155 &poll_handlers, 0, "Number of registered poll handlers");
156
157 static int polling = 0; /* global polling enable */
158 SYSCTL_UINT(_kern_polling, OID_AUTO, enable, CTLFLAG_RW,
159 &polling, 0, "Polling enabled");
160
161 static u_int32_t phase;
162 SYSCTL_UINT(_kern_polling, OID_AUTO, phase, CTLFLAG_RW,
163 &phase, 0, "Polling phase");
164
165 static u_int32_t suspect;
166 SYSCTL_UINT(_kern_polling, OID_AUTO, suspect, CTLFLAG_RW,
167 &suspect, 0, "suspect event");
168
169 static u_int32_t stalled;
170 SYSCTL_UINT(_kern_polling, OID_AUTO, stalled, CTLFLAG_RW,
171 &stalled, 0, "potential stalls");
172
173 static u_int32_t idlepoll_sleeping; /* idlepoll is sleeping */
174 SYSCTL_UINT(_kern_polling, OID_AUTO, idlepoll_sleeping, CTLFLAG_RD,
175 &idlepoll_sleeping, 0, "idlepoll is sleeping");
176
177
178 #define POLL_LIST_LEN 128
179 struct pollrec {
180 poll_handler_t *handler;
181 struct ifnet *ifp;
182 };
183
184 static struct pollrec pr[POLL_LIST_LEN];
185
186 static void
187 init_device_poll(void)
188 {
189
190 netisr_register(NETISR_POLL, (netisr_t *)netisr_poll, NULL, 0);
191 netisr_register(NETISR_POLLMORE, (netisr_t *)netisr_pollmore, NULL, 0);
192 }
193 SYSINIT(device_poll, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, init_device_poll, NULL)
194
195
196 /*
197 * Hook from hardclock. Tries to schedule a netisr, but keeps track
198 * of lost ticks due to the previous handler taking too long.
199 * Normally, this should not happen, because polling handler should
200 * run for a short time. However, in some cases (e.g. when there are
201 * changes in link status etc.) the drivers take a very long time
202 * (even in the order of milliseconds) to reset and reconfigure the
203 * device, causing apparent lost polls.
204 *
205 * The first part of the code is just for debugging purposes, and tries
206 * to count how often hardclock ticks are shorter than they should,
207 * meaning either stray interrupts or delayed events.
208 */
209 void
210 hardclock_device_poll(void)
211 {
212 static struct timeval prev_t, t;
213 int delta;
214
215 if (poll_handlers == 0)
216 return;
217
218 microuptime(&t);
219 delta = (t.tv_usec - prev_t.tv_usec) +
220 (t.tv_sec - prev_t.tv_sec)*1000000;
221 if (delta * hz < 500000)
222 short_ticks++;
223 else
224 prev_t = t;
225
226 if (pending_polls > 100) {
227 /*
228 * Too much, assume it has stalled (not always true
229 * see comment above).
230 */
231 stalled++;
232 pending_polls = 0;
233 phase = 0;
234 }
235
236 if (phase <= 2) {
237 if (phase != 0)
238 suspect++;
239 phase = 1;
240 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
241 phase = 2;
242 }
243 if (pending_polls++ > 0)
244 lost_polls++;
245 }
246
247 /*
248 * ether_poll is called from the idle loop or from the trap handler.
249 */
250 void
251 ether_poll(int count)
252 {
253 int i;
254
255 mtx_lock(&Giant);
256
257 if (count > poll_each_burst)
258 count = poll_each_burst;
259 for (i = 0 ; i < poll_handlers ; i++)
260 if (pr[i].handler && (IFF_UP|IFF_RUNNING) ==
261 (pr[i].ifp->if_flags & (IFF_UP|IFF_RUNNING)) )
262 pr[i].handler(pr[i].ifp, 0, count); /* quick check */
263 mtx_unlock(&Giant);
264 }
265
266 /*
267 * netisr_pollmore is called after other netisr's, possibly scheduling
268 * another NETISR_POLL call, or adapting the burst size for the next cycle.
269 *
270 * It is very bad to fetch large bursts of packets from a single card at once,
271 * because the burst could take a long time to be completely processed, or
272 * could saturate the intermediate queue (ipintrq or similar) leading to
273 * losses or unfairness. To reduce the problem, and also to account better for
274 * time spent in network-related processing, we split the burst in smaller
275 * chunks of fixed size, giving control to the other netisr's between chunks.
276 * This helps in improving the fairness, reducing livelock (because we
277 * emulate more closely the "process to completion" that we have with
278 * fastforwarding) and accounting for the work performed in low level
279 * handling and forwarding.
280 */
281
282 static struct timeval poll_start_t;
283
284 void
285 netisr_pollmore()
286 {
287 struct timeval t;
288 int kern_load;
289 /* XXX run at splhigh() or equivalent */
290
291 phase = 5;
292 if (residual_burst > 0) {
293 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
294 /* will run immediately on return, followed by netisrs */
295 return;
296 }
297 /* here we can account time spent in netisr's in this tick */
298 microuptime(&t);
299 kern_load = (t.tv_usec - poll_start_t.tv_usec) +
300 (t.tv_sec - poll_start_t.tv_sec)*1000000; /* us */
301 kern_load = (kern_load * hz) / 10000; /* 0..100 */
302 if (kern_load > (100 - user_frac)) { /* try decrease ticks */
303 if (poll_burst > 1)
304 poll_burst--;
305 } else {
306 if (poll_burst < poll_burst_max)
307 poll_burst++;
308 }
309
310 pending_polls--;
311 if (pending_polls == 0) /* we are done */
312 phase = 0;
313 else {
314 /*
315 * Last cycle was long and caused us to miss one or more
316 * hardclock ticks. Restart processing again, but slightly
317 * reduce the burst size to prevent that this happens again.
318 */
319 poll_burst -= (poll_burst / 8);
320 if (poll_burst < 1)
321 poll_burst = 1;
322 schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
323 phase = 6;
324 }
325 }
326
327 /*
328 * netisr_poll is scheduled by schednetisr when appropriate, typically once
329 * per tick. It is called at splnet() so first thing to do is to upgrade to
330 * splimp(), and call all registered handlers.
331 */
332 static void
333 netisr_poll(void)
334 {
335 static int reg_frac_count;
336 int i, cycles;
337 enum poll_cmd arg = POLL_ONLY;
338 mtx_lock(&Giant);
339
340 phase = 3;
341 if (residual_burst == 0) { /* first call in this tick */
342 microuptime(&poll_start_t);
343 /*
344 * Check that paremeters are consistent with runtime
345 * variables. Some of these tests could be done at sysctl
346 * time, but the savings would be very limited because we
347 * still have to check against reg_frac_count and
348 * poll_each_burst. So, instead of writing separate sysctl
349 * handlers, we do all here.
350 */
351
352 if (reg_frac > hz)
353 reg_frac = hz;
354 else if (reg_frac < 1)
355 reg_frac = 1;
356 if (reg_frac_count > reg_frac)
357 reg_frac_count = reg_frac - 1;
358 if (reg_frac_count-- == 0) {
359 arg = POLL_AND_CHECK_STATUS;
360 reg_frac_count = reg_frac - 1;
361 }
362 if (poll_burst_max < MIN_POLL_BURST_MAX)
363 poll_burst_max = MIN_POLL_BURST_MAX;
364 else if (poll_burst_max > MAX_POLL_BURST_MAX)
365 poll_burst_max = MAX_POLL_BURST_MAX;
366
367 if (poll_each_burst < 1)
368 poll_each_burst = 1;
369 else if (poll_each_burst > poll_burst_max)
370 poll_each_burst = poll_burst_max;
371
372 if (poll_burst > poll_burst_max)
373 poll_burst = poll_burst_max;
374 residual_burst = poll_burst;
375 }
376 cycles = (residual_burst < poll_each_burst) ?
377 residual_burst : poll_each_burst;
378 residual_burst -= cycles;
379
380 if (polling) {
381 for (i = 0 ; i < poll_handlers ; i++)
382 if (pr[i].handler && (IFF_UP|IFF_RUNNING) ==
383 (pr[i].ifp->if_flags & (IFF_UP|IFF_RUNNING)) )
384 pr[i].handler(pr[i].ifp, arg, cycles);
385 } else { /* unregister */
386 for (i = 0 ; i < poll_handlers ; i++) {
387 if (pr[i].handler &&
388 pr[i].ifp->if_flags & IFF_RUNNING) {
389 pr[i].ifp->if_flags &= ~IFF_POLLING;
390 pr[i].handler(pr[i].ifp, POLL_DEREGISTER, 1);
391 }
392 pr[i].handler=NULL;
393 }
394 residual_burst = 0;
395 poll_handlers = 0;
396 }
397 /* on -stable, schednetisr(NETISR_POLLMORE); */
398 phase = 4;
399 mtx_unlock(&Giant);
400 }
401
402 /*
403 * Try to register routine for polling. Returns 1 if successful
404 * (and polling should be enabled), 0 otherwise.
405 * A device is not supposed to register itself multiple times.
406 *
407 * This is called from within the *_intr() functions, so we do not need
408 * further locking.
409 */
410 int
411 ether_poll_register(poll_handler_t *h, struct ifnet *ifp)
412 {
413 int s;
414
415 if (polling == 0) /* polling disabled, cannot register */
416 return 0;
417 if (h == NULL || ifp == NULL) /* bad arguments */
418 return 0;
419 if ( !(ifp->if_flags & IFF_UP) ) /* must be up */
420 return 0;
421 if (ifp->if_flags & IFF_POLLING) /* already polling */
422 return 0;
423
424 s = splhigh();
425 if (poll_handlers >= POLL_LIST_LEN) {
426 /*
427 * List full, cannot register more entries.
428 * This should never happen; if it does, it is probably a
429 * broken driver trying to register multiple times. Checking
430 * this at runtime is expensive, and won't solve the problem
431 * anyways, so just report a few times and then give up.
432 */
433 static int verbose = 10 ;
434 splx(s);
435 if (verbose >0) {
436 printf("poll handlers list full, "
437 "maybe a broken driver ?\n");
438 verbose--;
439 }
440 return 0; /* no polling for you */
441 }
442
443 pr[poll_handlers].handler = h;
444 pr[poll_handlers].ifp = ifp;
445 poll_handlers++;
446 ifp->if_flags |= IFF_POLLING;
447 splx(s);
448 if (idlepoll_sleeping)
449 wakeup(&idlepoll_sleeping);
450 return 1; /* polling enabled in next call */
451 }
452
453 /*
454 * Remove interface from the polling list. Normally called by *_stop().
455 * It is not an error to call it with IFF_POLLING clear, the call is
456 * sufficiently rare to be preferable to save the space for the extra
457 * test in each driver in exchange of one additional function call.
458 */
459 int
460 ether_poll_deregister(struct ifnet *ifp)
461 {
462 int i;
463
464 mtx_lock(&Giant);
465 if ( !ifp || !(ifp->if_flags & IFF_POLLING) ) {
466 mtx_unlock(&Giant);
467 return 0;
468 }
469 for (i = 0 ; i < poll_handlers ; i++)
470 if (pr[i].ifp == ifp) /* found it */
471 break;
472 ifp->if_flags &= ~IFF_POLLING; /* found or not... */
473 if (i == poll_handlers) {
474 mtx_unlock(&Giant);
475 printf("ether_poll_deregister: ifp not found!!!\n");
476 return 0;
477 }
478 poll_handlers--;
479 if (i < poll_handlers) { /* Last entry replaces this one. */
480 pr[i].handler = pr[poll_handlers].handler;
481 pr[i].ifp = pr[poll_handlers].ifp;
482 }
483 mtx_unlock(&Giant);
484 return 1;
485 }
486
487 static void
488 poll_idle(void)
489 {
490 struct thread *td = curthread;
491 struct rtprio rtp;
492 int pri;
493
494 rtp.prio = RTP_PRIO_MAX; /* lowest priority */
495 rtp.type = RTP_PRIO_IDLE;
496 mtx_lock_spin(&sched_lock);
497 rtp_to_pri(&rtp, td->td_ksegrp);
498 pri = td->td_priority;
499 mtx_unlock_spin(&sched_lock);
500
501 for (;;) {
502 if (poll_in_idle_loop && poll_handlers > 0) {
503 idlepoll_sleeping = 0;
504 mtx_lock(&Giant);
505 ether_poll(poll_each_burst);
506 mtx_unlock(&Giant);
507 mtx_assert(&Giant, MA_NOTOWNED);
508 mtx_lock_spin(&sched_lock);
509 mi_switch(SW_VOL, NULL);
510 mtx_unlock_spin(&sched_lock);
511 } else {
512 idlepoll_sleeping = 1;
513 tsleep(&idlepoll_sleeping, pri, "pollid", hz * 3);
514 }
515 }
516 }
517
518 static struct proc *idlepoll;
519 static struct kproc_desc idlepoll_kp = {
520 "idlepoll",
521 poll_idle,
522 &idlepoll
523 };
524 SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start, &idlepoll_kp)
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