Messages in this thread | | | Date | Mon, 9 Nov 2015 11:36:06 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 2/2] sched: consider missed ticks in full NOHZ |
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On Mon, Nov 09, 2015 at 11:36:54AM +0900, Byungchul Park wrote: > 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@lge.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?
I was thinking of getting rid of rq->last_load_update_tick entirely. If we can pass in how many (local) ticks were lost on this cpu, we don't have to rely on the jiffy counter at all.
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