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Date: Wed, 29 Apr 2009 09:34:49 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, mingo@...e.hu,
akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
davem@...emloft.net, dada1@...mosbay.com, zbr@...emap.net,
jeff.chua.linux@...il.com, paulus@...ba.org, laijs@...fujitsu.com,
jengelh@...ozas.de, r000n@...0n.net, benh@...nel.crashing.org
Subject: Re: [PATCH RFC] v2 not-so-expedited "big hammer" RCU grace periods
* Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> On Wed, Apr 29, 2009 at 01:58:40AM -0400, Mathieu Desnoyers wrote:
> > * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
>
> [ . . . ]
>
> > > +
> > > + /*
> > > + * Wait a bit. If we have already waited a fair
> > > + * amount of time, sleep.
> > > + */
> > > + if (++times < 10)
> > > + udelay(10 * times);
> > > + else
> > > + schedule_timeout_uninterruptible(1);
> >
> > Waiting a whole jiffy (e.g. 1ms, 4ms, 10ms) here seems like a big hammer
> > to nail a delicate pin. I would not be surprised if your long delay
> > would come from here. Is it possible that your ipi+scheduling delay is
> > actually longer than the 11 udelays you are doing and that you end up
> > calling schedule_timeout_uninterruptible(1) each time ?
>
> It might be -- easy to try increasing the number of udelay passes
> through the loop.
>
Or just counting the number of times schedule_timeout_uninterruptible()
is invoked from here.
> On the other hand, the 550 microseconds waited by the sum of the udelay
> passes is ridiculously long in and of itself.
>
> Still, would be interesting to know. I will change the loop to udelay
> up to HZ. Hmmm... I wonder if udelay() itself is turning into a 1-HZ
> wait beyond a certain point.
>
It does not seem to be the case in arch/x86/lib/delay.c at least.
Mathieu
> Thanx, Paul
>
> > Mathieu
> >
> > > + /* FIXME: need to complain about holdout CPUs if too long. */
> > > + }
> > > +
> > > + synchronize_rcu_bh_completed++;
> > > + mutex_unlock(&synchronize_rcu_bh_mutex);
> > > +}
> > > +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
> > > +
> > > +void synchronize_rcu_bh_expedited(void)
> > > +{
> > > + synchronize_rcu_expedited();
> > > +}
> > > +EXPORT_SYMBOL_GPL(synchronize_rcu_bh_expedited);
> > > +
> > > +#endif /* #else #ifndef CONFIG_SMP */
> > > +
> > > void __init rcu_init(void)
> > > {
> > > __rcu_init();
> > > hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
> > > + synchronize_rcu_expedited_init();
> > > }
> > >
> > > void rcu_scheduler_starting(void)
> > > diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> > > index 9b4a975..8845936 100644
> > > --- a/kernel/rcutorture.c
> > > +++ b/kernel/rcutorture.c
> > > @@ -257,14 +257,14 @@ struct rcu_torture_ops {
> > > void (*init)(void);
> > > void (*cleanup)(void);
> > > int (*readlock)(void);
> > > - void (*readdelay)(struct rcu_random_state *rrsp);
> > > + void (*read_delay)(struct rcu_random_state *rrsp);
> > > void (*readunlock)(int idx);
> > > int (*completed)(void);
> > > - void (*deferredfree)(struct rcu_torture *p);
> > > + void (*deferred_free)(struct rcu_torture *p);
> > > void (*sync)(void);
> > > void (*cb_barrier)(void);
> > > int (*stats)(char *page);
> > > - int irqcapable;
> > > + int irq_capable;
> > > char *name;
> > > };
> > > static struct rcu_torture_ops *cur_ops = NULL;
> > > @@ -320,7 +320,7 @@ rcu_torture_cb(struct rcu_head *p)
> > > rp->rtort_mbtest = 0;
> > > rcu_torture_free(rp);
> > > } else
> > > - cur_ops->deferredfree(rp);
> > > + cur_ops->deferred_free(rp);
> > > }
> > >
> > > static void rcu_torture_deferred_free(struct rcu_torture *p)
> > > @@ -329,18 +329,18 @@ static void rcu_torture_deferred_free(struct rcu_torture *p)
> > > }
> > >
> > > static struct rcu_torture_ops rcu_ops = {
> > > - .init = NULL,
> > > - .cleanup = NULL,
> > > - .readlock = rcu_torture_read_lock,
> > > - .readdelay = rcu_read_delay,
> > > - .readunlock = rcu_torture_read_unlock,
> > > - .completed = rcu_torture_completed,
> > > - .deferredfree = rcu_torture_deferred_free,
> > > - .sync = synchronize_rcu,
> > > - .cb_barrier = rcu_barrier,
> > > - .stats = NULL,
> > > - .irqcapable = 1,
> > > - .name = "rcu"
> > > + .init = NULL,
> > > + .cleanup = NULL,
> > > + .readlock = rcu_torture_read_lock,
> > > + .read_delay = rcu_read_delay,
> > > + .readunlock = rcu_torture_read_unlock,
> > > + .completed = rcu_torture_completed,
> > > + .deferred_free = rcu_torture_deferred_free,
> > > + .sync = synchronize_rcu,
> > > + .cb_barrier = rcu_barrier,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "rcu"
> > > };
> > >
> > > static void rcu_sync_torture_deferred_free(struct rcu_torture *p)
> > > @@ -370,18 +370,18 @@ static void rcu_sync_torture_init(void)
> > > }
> > >
> > > static struct rcu_torture_ops rcu_sync_ops = {
> > > - .init = rcu_sync_torture_init,
> > > - .cleanup = NULL,
> > > - .readlock = rcu_torture_read_lock,
> > > - .readdelay = rcu_read_delay,
> > > - .readunlock = rcu_torture_read_unlock,
> > > - .completed = rcu_torture_completed,
> > > - .deferredfree = rcu_sync_torture_deferred_free,
> > > - .sync = synchronize_rcu,
> > > - .cb_barrier = NULL,
> > > - .stats = NULL,
> > > - .irqcapable = 1,
> > > - .name = "rcu_sync"
> > > + .init = rcu_sync_torture_init,
> > > + .cleanup = NULL,
> > > + .readlock = rcu_torture_read_lock,
> > > + .read_delay = rcu_read_delay,
> > > + .readunlock = rcu_torture_read_unlock,
> > > + .completed = rcu_torture_completed,
> > > + .deferred_free = rcu_sync_torture_deferred_free,
> > > + .sync = synchronize_rcu,
> > > + .cb_barrier = NULL,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "rcu_sync"
> > > };
> > >
> > > /*
> > > @@ -432,33 +432,53 @@ static void rcu_bh_torture_synchronize(void)
> > > }
> > >
> > > static struct rcu_torture_ops rcu_bh_ops = {
> > > - .init = NULL,
> > > - .cleanup = NULL,
> > > - .readlock = rcu_bh_torture_read_lock,
> > > - .readdelay = rcu_read_delay, /* just reuse rcu's version. */
> > > - .readunlock = rcu_bh_torture_read_unlock,
> > > - .completed = rcu_bh_torture_completed,
> > > - .deferredfree = rcu_bh_torture_deferred_free,
> > > - .sync = rcu_bh_torture_synchronize,
> > > - .cb_barrier = rcu_barrier_bh,
> > > - .stats = NULL,
> > > - .irqcapable = 1,
> > > - .name = "rcu_bh"
> > > + .init = NULL,
> > > + .cleanup = NULL,
> > > + .readlock = rcu_bh_torture_read_lock,
> > > + .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > > + .readunlock = rcu_bh_torture_read_unlock,
> > > + .completed = rcu_bh_torture_completed,
> > > + .deferred_free = rcu_bh_torture_deferred_free,
> > > + .sync = rcu_bh_torture_synchronize,
> > > + .cb_barrier = rcu_barrier_bh,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "rcu_bh"
> > > };
> > >
> > > static struct rcu_torture_ops rcu_bh_sync_ops = {
> > > - .init = rcu_sync_torture_init,
> > > - .cleanup = NULL,
> > > - .readlock = rcu_bh_torture_read_lock,
> > > - .readdelay = rcu_read_delay, /* just reuse rcu's version. */
> > > - .readunlock = rcu_bh_torture_read_unlock,
> > > - .completed = rcu_bh_torture_completed,
> > > - .deferredfree = rcu_sync_torture_deferred_free,
> > > - .sync = rcu_bh_torture_synchronize,
> > > - .cb_barrier = NULL,
> > > - .stats = NULL,
> > > - .irqcapable = 1,
> > > - .name = "rcu_bh_sync"
> > > + .init = rcu_sync_torture_init,
> > > + .cleanup = NULL,
> > > + .readlock = rcu_bh_torture_read_lock,
> > > + .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > > + .readunlock = rcu_bh_torture_read_unlock,
> > > + .completed = rcu_bh_torture_completed,
> > > + .deferred_free = rcu_sync_torture_deferred_free,
> > > + .sync = rcu_bh_torture_synchronize,
> > > + .cb_barrier = NULL,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "rcu_bh_sync"
> > > +};
> > > +
> > > +static int rcu_bh_expedited_torture_completed(void)
> > > +{
> > > + return rcu_batches_completed_bh_expedited();
> > > +}
> > > +
> > > +static struct rcu_torture_ops rcu_bh_expedited_ops = {
> > > + .init = rcu_sync_torture_init,
> > > + .cleanup = NULL,
> > > + .readlock = rcu_bh_torture_read_lock,
> > > + .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > > + .readunlock = rcu_bh_torture_read_unlock,
> > > + .completed = rcu_bh_expedited_torture_completed,
> > > + .deferred_free = rcu_sync_torture_deferred_free,
> > > + .sync = synchronize_rcu_bh_expedited,
> > > + .cb_barrier = NULL,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "rcu_bh_expedited"
> > > };
> > >
> > > /*
> > > @@ -530,17 +550,17 @@ static int srcu_torture_stats(char *page)
> > > }
> > >
> > > static struct rcu_torture_ops srcu_ops = {
> > > - .init = srcu_torture_init,
> > > - .cleanup = srcu_torture_cleanup,
> > > - .readlock = srcu_torture_read_lock,
> > > - .readdelay = srcu_read_delay,
> > > - .readunlock = srcu_torture_read_unlock,
> > > - .completed = srcu_torture_completed,
> > > - .deferredfree = rcu_sync_torture_deferred_free,
> > > - .sync = srcu_torture_synchronize,
> > > - .cb_barrier = NULL,
> > > - .stats = srcu_torture_stats,
> > > - .name = "srcu"
> > > + .init = srcu_torture_init,
> > > + .cleanup = srcu_torture_cleanup,
> > > + .readlock = srcu_torture_read_lock,
> > > + .read_delay = srcu_read_delay,
> > > + .readunlock = srcu_torture_read_unlock,
> > > + .completed = srcu_torture_completed,
> > > + .deferred_free = rcu_sync_torture_deferred_free,
> > > + .sync = srcu_torture_synchronize,
> > > + .cb_barrier = NULL,
> > > + .stats = srcu_torture_stats,
> > > + .name = "srcu"
> > > };
> > >
> > > /*
> > > @@ -574,32 +594,32 @@ static void sched_torture_synchronize(void)
> > > }
> > >
> > > static struct rcu_torture_ops sched_ops = {
> > > - .init = rcu_sync_torture_init,
> > > - .cleanup = NULL,
> > > - .readlock = sched_torture_read_lock,
> > > - .readdelay = rcu_read_delay, /* just reuse rcu's version. */
> > > - .readunlock = sched_torture_read_unlock,
> > > - .completed = sched_torture_completed,
> > > - .deferredfree = rcu_sched_torture_deferred_free,
> > > - .sync = sched_torture_synchronize,
> > > - .cb_barrier = rcu_barrier_sched,
> > > - .stats = NULL,
> > > - .irqcapable = 1,
> > > - .name = "sched"
> > > + .init = rcu_sync_torture_init,
> > > + .cleanup = NULL,
> > > + .readlock = sched_torture_read_lock,
> > > + .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > > + .readunlock = sched_torture_read_unlock,
> > > + .completed = sched_torture_completed,
> > > + .deferred_free = rcu_sched_torture_deferred_free,
> > > + .sync = sched_torture_synchronize,
> > > + .cb_barrier = rcu_barrier_sched,
> > > + .stats = NULL,
> > > + .irq_capable = 1,
> > > + .name = "sched"
> > > };
> > >
> > > static struct rcu_torture_ops sched_ops_sync = {
> > > - .init = rcu_sync_torture_init,
> > > - .cleanup = NULL,
> > > - .readlock = sched_torture_read_lock,
> > > - .readdelay = rcu_read_delay, /* just reuse rcu's version. */
> > > - .readunlock = sched_torture_read_unlock,
> > > - .completed = sched_torture_completed,
> > > - .deferredfree = rcu_sync_torture_deferred_free,
> > > - .sync = sched_torture_synchronize,
> > > - .cb_barrier = NULL,
> > > - .stats = NULL,
> > > - .name = "sched_sync"
> > > + .init = rcu_sync_torture_init,
> > > + .cleanup = NULL,
> > > + .readlock = sched_torture_read_lock,
> > > + .read_delay = rcu_read_delay, /* just reuse rcu's version. */
> > > + .readunlock = sched_torture_read_unlock,
> > > + .completed = sched_torture_completed,
> > > + .deferred_free = rcu_sync_torture_deferred_free,
> > > + .sync = sched_torture_synchronize,
> > > + .cb_barrier = NULL,
> > > + .stats = NULL,
> > > + .name = "sched_sync"
> > > };
> > >
> > > /*
> > > @@ -635,7 +655,7 @@ rcu_torture_writer(void *arg)
> > > i = RCU_TORTURE_PIPE_LEN;
> > > atomic_inc(&rcu_torture_wcount[i]);
> > > old_rp->rtort_pipe_count++;
> > > - cur_ops->deferredfree(old_rp);
> > > + cur_ops->deferred_free(old_rp);
> > > }
> > > rcu_torture_current_version++;
> > > oldbatch = cur_ops->completed();
> > > @@ -700,7 +720,7 @@ static void rcu_torture_timer(unsigned long unused)
> > > if (p->rtort_mbtest == 0)
> > > atomic_inc(&n_rcu_torture_mberror);
> > > spin_lock(&rand_lock);
> > > - cur_ops->readdelay(&rand);
> > > + cur_ops->read_delay(&rand);
> > > n_rcu_torture_timers++;
> > > spin_unlock(&rand_lock);
> > > preempt_disable();
> > > @@ -738,11 +758,11 @@ rcu_torture_reader(void *arg)
> > >
> > > VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
> > > set_user_nice(current, 19);
> > > - if (irqreader && cur_ops->irqcapable)
> > > + if (irqreader && cur_ops->irq_capable)
> > > setup_timer_on_stack(&t, rcu_torture_timer, 0);
> > >
> > > do {
> > > - if (irqreader && cur_ops->irqcapable) {
> > > + if (irqreader && cur_ops->irq_capable) {
> > > if (!timer_pending(&t))
> > > mod_timer(&t, 1);
> > > }
> > > @@ -757,7 +777,7 @@ rcu_torture_reader(void *arg)
> > > }
> > > if (p->rtort_mbtest == 0)
> > > atomic_inc(&n_rcu_torture_mberror);
> > > - cur_ops->readdelay(&rand);
> > > + cur_ops->read_delay(&rand);
> > > preempt_disable();
> > > pipe_count = p->rtort_pipe_count;
> > > if (pipe_count > RCU_TORTURE_PIPE_LEN) {
> > > @@ -778,7 +798,7 @@ rcu_torture_reader(void *arg)
> > > } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
> > > VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
> > > rcutorture_shutdown_absorb("rcu_torture_reader");
> > > - if (irqreader && cur_ops->irqcapable)
> > > + if (irqreader && cur_ops->irq_capable)
> > > del_timer_sync(&t);
> > > while (!kthread_should_stop())
> > > schedule_timeout_uninterruptible(1);
> > > @@ -1078,6 +1098,7 @@ rcu_torture_init(void)
> > > int firsterr = 0;
> > > static struct rcu_torture_ops *torture_ops[] =
> > > { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
> > > + &rcu_bh_expedited_ops,
> > > &srcu_ops, &sched_ops, &sched_ops_sync, };
> > >
> > > mutex_lock(&fullstop_mutex);
> > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > > index d2a372f..bf2c21d 100644
> > > --- a/kernel/rcutree.c
> > > +++ b/kernel/rcutree.c
> > > @@ -89,6 +89,7 @@ void rcu_qsctr_inc(int cpu)
> > > struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
> > > rdp->passed_quiesc = 1;
> > > rdp->passed_quiesc_completed = rdp->completed;
> > > + synchronize_rcu_expedited_qs(cpu);
> > > }
> > >
> > > void rcu_bh_qsctr_inc(int cpu)
> >
> > --
> > Mathieu Desnoyers
> > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
> > --
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--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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