debuggers.hg

view xen/common/rcupdate.c @ 22906:700ac6445812

Now add KDB to the non-kdb tree
author Mukesh Rathor
date Thu Feb 03 15:42:41 2011 -0800 (2011-02-03)
parents 75b6287626ee
children
line source
1 /*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright (C) IBM Corporation, 2001
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 *
23 * Modifications for Xen: Jose Renato Santos
24 * Copyright (C) Hewlett-Packard, 2006
25 *
26 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
27 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
28 * Papers:
29 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
30 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
31 *
32 * For detailed explanation of Read-Copy Update mechanism see -
33 * http://lse.sourceforge.net/locking/rcupdate.html
34 */
35 #include <xen/types.h>
36 #include <xen/kernel.h>
37 #include <xen/init.h>
38 #include <xen/spinlock.h>
39 #include <xen/smp.h>
40 #include <xen/rcupdate.h>
41 #include <xen/sched.h>
42 #include <asm/atomic.h>
43 #include <xen/bitops.h>
44 #include <xen/percpu.h>
45 #include <xen/softirq.h>
46 #include <xen/cpu.h>
47 #include <xen/stop_machine.h>
49 /* Definition for rcupdate control block. */
50 struct rcu_ctrlblk rcu_ctrlblk = {
51 .cur = -300,
52 .completed = -300,
53 .lock = SPIN_LOCK_UNLOCKED,
54 .cpumask = CPU_MASK_NONE,
55 };
57 DEFINE_PER_CPU(struct rcu_data, rcu_data);
59 static int blimit = 10;
60 static int qhimark = 10000;
61 static int qlowmark = 100;
62 static int rsinterval = 1000;
64 struct rcu_barrier_data {
65 struct rcu_head head;
66 atomic_t *cpu_count;
67 };
69 static void rcu_barrier_callback(struct rcu_head *head)
70 {
71 struct rcu_barrier_data *data = container_of(
72 head, struct rcu_barrier_data, head);
73 atomic_inc(data->cpu_count);
74 }
76 static int rcu_barrier_action(void *_cpu_count)
77 {
78 struct rcu_barrier_data data = { .cpu_count = _cpu_count };
80 ASSERT(!local_irq_is_enabled());
81 local_irq_enable();
83 /*
84 * When callback is executed, all previously-queued RCU work on this CPU
85 * is completed. When all CPUs have executed their callback, data.cpu_count
86 * will have been incremented to include every online CPU.
87 */
88 call_rcu(&data.head, rcu_barrier_callback);
90 while ( atomic_read(data.cpu_count) != cpus_weight(cpu_online_map) )
91 {
92 process_pending_softirqs();
93 cpu_relax();
94 }
96 local_irq_disable();
98 return 0;
99 }
101 int rcu_barrier(void)
102 {
103 atomic_t cpu_count = ATOMIC_INIT(0);
104 return stop_machine_run(rcu_barrier_action, &cpu_count, NR_CPUS);
105 }
107 static void force_quiescent_state(struct rcu_data *rdp,
108 struct rcu_ctrlblk *rcp)
109 {
110 cpumask_t cpumask;
111 raise_softirq(SCHEDULE_SOFTIRQ);
112 if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
113 rdp->last_rs_qlen = rdp->qlen;
114 /*
115 * Don't send IPI to itself. With irqs disabled,
116 * rdp->cpu is the current cpu.
117 */
118 cpumask = rcp->cpumask;
119 cpu_clear(rdp->cpu, cpumask);
120 cpumask_raise_softirq(cpumask, SCHEDULE_SOFTIRQ);
121 }
122 }
124 /**
125 * call_rcu - Queue an RCU callback for invocation after a grace period.
126 * @head: structure to be used for queueing the RCU updates.
127 * @func: actual update function to be invoked after the grace period
128 *
129 * The update function will be invoked some time after a full grace
130 * period elapses, in other words after all currently executing RCU
131 * read-side critical sections have completed. RCU read-side critical
132 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
133 * and may be nested.
134 */
135 void fastcall call_rcu(struct rcu_head *head,
136 void (*func)(struct rcu_head *rcu))
137 {
138 unsigned long flags;
139 struct rcu_data *rdp;
141 head->func = func;
142 head->next = NULL;
143 local_irq_save(flags);
144 rdp = &__get_cpu_var(rcu_data);
145 *rdp->nxttail = head;
146 rdp->nxttail = &head->next;
147 if (unlikely(++rdp->qlen > qhimark)) {
148 rdp->blimit = INT_MAX;
149 force_quiescent_state(rdp, &rcu_ctrlblk);
150 }
151 local_irq_restore(flags);
152 }
154 /*
155 * Invoke the completed RCU callbacks. They are expected to be in
156 * a per-cpu list.
157 */
158 static void rcu_do_batch(struct rcu_data *rdp)
159 {
160 struct rcu_head *next, *list;
161 int count = 0;
163 list = rdp->donelist;
164 while (list) {
165 next = rdp->donelist = list->next;
166 list->func(list);
167 list = next;
168 rdp->qlen--;
169 if (++count >= rdp->blimit)
170 break;
171 }
172 if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
173 rdp->blimit = blimit;
174 if (!rdp->donelist)
175 rdp->donetail = &rdp->donelist;
176 else
177 raise_softirq(RCU_SOFTIRQ);
178 }
180 /*
181 * Grace period handling:
182 * The grace period handling consists out of two steps:
183 * - A new grace period is started.
184 * This is done by rcu_start_batch. The start is not broadcasted to
185 * all cpus, they must pick this up by comparing rcp->cur with
186 * rdp->quiescbatch. All cpus are recorded in the
187 * rcu_ctrlblk.cpumask bitmap.
188 * - All cpus must go through a quiescent state.
189 * Since the start of the grace period is not broadcasted, at least two
190 * calls to rcu_check_quiescent_state are required:
191 * The first call just notices that a new grace period is running. The
192 * following calls check if there was a quiescent state since the beginning
193 * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
194 * the bitmap is empty, then the grace period is completed.
195 * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
196 * period (if necessary).
197 */
198 /*
199 * Register a new batch of callbacks, and start it up if there is currently no
200 * active batch and the batch to be registered has not already occurred.
201 * Caller must hold rcu_ctrlblk.lock.
202 */
203 static void rcu_start_batch(struct rcu_ctrlblk *rcp)
204 {
205 if (rcp->next_pending &&
206 rcp->completed == rcp->cur) {
207 rcp->next_pending = 0;
208 /*
209 * next_pending == 0 must be visible in
210 * __rcu_process_callbacks() before it can see new value of cur.
211 */
212 smp_wmb();
213 rcp->cur++;
215 rcp->cpumask = cpu_online_map;
216 }
217 }
219 /*
220 * cpu went through a quiescent state since the beginning of the grace period.
221 * Clear it from the cpu mask and complete the grace period if it was the last
222 * cpu. Start another grace period if someone has further entries pending
223 */
224 static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
225 {
226 cpu_clear(cpu, rcp->cpumask);
227 if (cpus_empty(rcp->cpumask)) {
228 /* batch completed ! */
229 rcp->completed = rcp->cur;
230 rcu_start_batch(rcp);
231 }
232 }
234 /*
235 * Check if the cpu has gone through a quiescent state (say context
236 * switch). If so and if it already hasn't done so in this RCU
237 * quiescent cycle, then indicate that it has done so.
238 */
239 static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
240 struct rcu_data *rdp)
241 {
242 if (rdp->quiescbatch != rcp->cur) {
243 /* start new grace period: */
244 rdp->qs_pending = 1;
245 rdp->quiescbatch = rcp->cur;
246 return;
247 }
249 /* Grace period already completed for this cpu?
250 * qs_pending is checked instead of the actual bitmap to avoid
251 * cacheline trashing.
252 */
253 if (!rdp->qs_pending)
254 return;
256 rdp->qs_pending = 0;
258 spin_lock(&rcp->lock);
259 /*
260 * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
261 * during cpu startup. Ignore the quiescent state.
262 */
263 if (likely(rdp->quiescbatch == rcp->cur))
264 cpu_quiet(rdp->cpu, rcp);
266 spin_unlock(&rcp->lock);
267 }
270 /*
271 * This does the RCU processing work from softirq context.
272 */
273 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
274 struct rcu_data *rdp)
275 {
276 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
277 *rdp->donetail = rdp->curlist;
278 rdp->donetail = rdp->curtail;
279 rdp->curlist = NULL;
280 rdp->curtail = &rdp->curlist;
281 }
283 local_irq_disable();
284 if (rdp->nxtlist && !rdp->curlist) {
285 rdp->curlist = rdp->nxtlist;
286 rdp->curtail = rdp->nxttail;
287 rdp->nxtlist = NULL;
288 rdp->nxttail = &rdp->nxtlist;
289 local_irq_enable();
291 /*
292 * start the next batch of callbacks
293 */
295 /* determine batch number */
296 rdp->batch = rcp->cur + 1;
297 /* see the comment and corresponding wmb() in
298 * the rcu_start_batch()
299 */
300 smp_rmb();
302 if (!rcp->next_pending) {
303 /* and start it/schedule start if it's a new batch */
304 spin_lock(&rcp->lock);
305 rcp->next_pending = 1;
306 rcu_start_batch(rcp);
307 spin_unlock(&rcp->lock);
308 }
309 } else {
310 local_irq_enable();
311 }
312 rcu_check_quiescent_state(rcp, rdp);
313 if (rdp->donelist)
314 rcu_do_batch(rdp);
315 }
317 static void rcu_process_callbacks(void)
318 {
319 __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
320 }
322 static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
323 {
324 /* This cpu has pending rcu entries and the grace period
325 * for them has completed.
326 */
327 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
328 return 1;
330 /* This cpu has no pending entries, but there are new entries */
331 if (!rdp->curlist && rdp->nxtlist)
332 return 1;
334 /* This cpu has finished callbacks to invoke */
335 if (rdp->donelist)
336 return 1;
338 /* The rcu core waits for a quiescent state from the cpu */
339 if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
340 return 1;
342 /* nothing to do */
343 return 0;
344 }
346 int rcu_pending(int cpu)
347 {
348 return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu));
349 }
351 /*
352 * Check to see if any future RCU-related work will need to be done
353 * by the current CPU, even if none need be done immediately, returning
354 * 1 if so. This function is part of the RCU implementation; it is -not-
355 * an exported member of the RCU API.
356 */
357 int rcu_needs_cpu(int cpu)
358 {
359 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
361 return (!!rdp->curlist || rcu_pending(cpu));
362 }
364 void rcu_check_callbacks(int cpu)
365 {
366 raise_softirq(RCU_SOFTIRQ);
367 }
369 static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
370 struct rcu_head **tail)
371 {
372 local_irq_disable();
373 *this_rdp->nxttail = list;
374 if (list)
375 this_rdp->nxttail = tail;
376 local_irq_enable();
377 }
379 static void rcu_offline_cpu(struct rcu_data *this_rdp,
380 struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
381 {
382 /* If the cpu going offline owns the grace period we can block
383 * indefinitely waiting for it, so flush it here.
384 */
385 spin_lock(&rcp->lock);
386 if (rcp->cur != rcp->completed)
387 cpu_quiet(rdp->cpu, rcp);
388 spin_unlock(&rcp->lock);
390 rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
391 rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
392 rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
394 local_irq_disable();
395 this_rdp->qlen += rdp->qlen;
396 local_irq_enable();
397 }
399 static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
400 struct rcu_data *rdp)
401 {
402 memset(rdp, 0, sizeof(*rdp));
403 rdp->curtail = &rdp->curlist;
404 rdp->nxttail = &rdp->nxtlist;
405 rdp->donetail = &rdp->donelist;
406 rdp->quiescbatch = rcp->completed;
407 rdp->qs_pending = 0;
408 rdp->cpu = cpu;
409 rdp->blimit = blimit;
410 }
412 static int cpu_callback(
413 struct notifier_block *nfb, unsigned long action, void *hcpu)
414 {
415 unsigned int cpu = (unsigned long)hcpu;
416 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
418 switch ( action )
419 {
420 case CPU_UP_PREPARE:
421 rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
422 break;
423 case CPU_UP_CANCELED:
424 case CPU_DEAD:
425 rcu_offline_cpu(&this_cpu(rcu_data), &rcu_ctrlblk, rdp);
426 break;
427 default:
428 break;
429 }
431 return NOTIFY_DONE;
432 }
434 static struct notifier_block cpu_nfb = {
435 .notifier_call = cpu_callback
436 };
438 void __init rcu_init(void)
439 {
440 void *cpu = (void *)(long)smp_processor_id();
441 cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
442 register_cpu_notifier(&cpu_nfb);
443 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
444 }