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Date: Mon, 9 Nov 2015 11:36:54 +0900 From: Byungchul Park <byungchul.park@....com> To: Peter Zijlstra <peterz@...radead.org> Cc: mingo@...nel.org, linux-kernel@...r.kernel.org, fweisbec@...il.com, tglx@...utronix.de Subject: Re: [PATCH v4 2/2] sched: consider missed ticks in full NOHZ On Mon, Nov 02, 2015 at 05:10:16PM +0100, Peter Zijlstra wrote: > On Wed, Oct 14, 2015 at 06:47:36PM +0900, byungchul.park@....com wrote: > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -4428,7 +4428,7 @@ static void update_idle_cpu_load(struct rq *this_rq) > > So if one were to read the comment above update_idle_cpu_load() one > would find there's a problem with jiffy based accounting. > > > /* > > * Called from tick_nohz_idle_exit() -- try and fix up the ticks we missed. > > */ > > -void update_cpu_load_nohz(void) > > +void update_cpu_load_nohz(int active) > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index 7c7ec45..515edf3 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > > -static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) > > +static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int active) > > { > > /* Update jiffies first */ > > tick_do_update_jiffies64(now); > > - update_cpu_load_nohz(); > > + update_cpu_load_nohz(active); > > > > calc_load_exit_idle(); > > touch_softlockup_watchdog(); > > And we could solve all that nicely if we pull up the hrtimer_forward() > result from tick_nohz_restart(), that way we have the actual number of > ticks lost on this cpu, and no need to start guessing about it. hello, are you talking about the lag between writer and reader for jiffies? i think your proposal can solve the problem of update_cpu_load_nohz(). but it's still hard to care the cases of update_idle_cpu_load() and update_cpu_load_active() even by the way you proposed. do you think it would be ok even if it solves only one case? update_idle_cpu_load() still need to guess about it. is there something i missed? or did i mis-understand what you intend? > > Hmm? > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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