Messages in this thread Patch in this message | | | Date | Tue, 27 May 2014 19:30:50 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] tracing: Don't account for cpu idle time with irqsoff tracers |
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On Tue, 27 May 2014 15:21:39 -0700 Stephen Boyd <sboyd@codeaurora.org> wrote:
> > Arnd brings up a good point. > > Hrm.. still not getting Arnd's mails.
Strange. What mail service do you have. Could they be blocking him?
> > > If we disable irqs off tracing completely, > > we may be missing places in the idle path that disable interrupts for > > long periods of time. We may want to move the stop down further. > > > > The way it works (IIRC), and why tracing can start again is that it can > > nest. Perhaps we need to stop it further down if we can't move it > > completely. > > > > I'm not sure how much deeper it can go and I'm afraid it will become a > game of whack-a-mole. I already see two places that disable and reenable > irqs after stop_critical_timings() is called (first in rcu_idle_enter() > and second in clockevents_notify()). Should rcu_idle_enter() move to > raw_local_irq_save()? It looks like that path calls rcu_sched_qs() and > on tiny RCU that again needs the raw_ treatement. We can probably call > stop_critical_timings() after rcu_idle_enter() to fix this.
I don't think we need to whack-a-mole. The start stop should be around where it goes to sleep.
> > What about clockevents_notify? __raw_spin_lock_irqsave() should probably > use raw_local_irqsave().
No that solution is even worse. We need lockdep working here.
> > If we go the raw route, do we even need stop/start_critical_timings()? > Can't we just use raw accessors in the idle paths > (tick_nohz_idle_{enter,exit}(), cpuidle_enter(), etc.) and get rid of > the stop/start stuff completely? I admit this patch is pretty much a big > sledge hammer that tries to make things simple, but if there is some > benefit to the raw accessors I'm willing to send patches to fix all the > call sites. >
How about the following. I don't see any reason stop_critical_timings() can't be called from within rcu_idle code, as it doesn't use any rcu.
Paul, Peter, see anything wrong with this?
-- Steve
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 8f4390a..f5e6a64 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -88,12 +88,6 @@ static int cpuidle_idle_call(void) } /* - * During the idle period, stop measuring the disabled irqs - * critical sections latencies - */ - stop_critical_timings(); - - /* * Tell the RCU framework we are entering an idle section, * so no more rcu read side critical sections and one more * step to the grace period @@ -144,6 +138,12 @@ static int cpuidle_idle_call(void) trace_cpu_idle_rcuidle(next_state, dev->cpu); /* + * During the idle period, stop measuring the + * disabled irqs critical sections latencies + */ + stop_critical_timings(); + + /* * Enter the idle state previously * returned by the governor * decision. This function will block @@ -154,6 +154,8 @@ static int cpuidle_idle_call(void) entered_state = cpuidle_enter(drv, dev, next_state); + start_critical_timings(); + trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); @@ -175,8 +177,11 @@ static int cpuidle_idle_call(void) * We can't use the cpuidle framework, let's use the default * idle routine */ - if (ret) + if (ret) { + stop_critical_timings(); arch_cpu_idle(); + start_critical_timings(); + } __current_set_polling(); @@ -188,7 +193,6 @@ static int cpuidle_idle_call(void) local_irq_enable(); rcu_idle_exit(); - start_critical_timings(); return 0; }
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