Good morning,
On Tue, 2016-01-26 at 13:20 -0600, Christoph Lameter wrote:
> On Tue, 26 Jan 2016, Mike Galbraith wrote:
>
> > > The system going idle is a fastpath. Mind boogling.
> >
> > Hohum, noted. Now what about those cycles, and the sleeping lock you
> > injected for -rt?
>
> Since we (the NOHZ people) care mostly about NOHZ then lets restrict
> that to the NOHZ mode. Then it should not affect your load.
Tons of folks do have NO_HZ enabled (including me). Isn't there a spot
somewhere in NO_HZ_FULL code where it can take up residence? (one with
a tad lower maximum call frequency would be good, a nohz_full cpu isn't
necessarily being used for pure compute exclusively)
> Subject: Move quiet_vmstat() to NOHZ code
>
> quiet_vmstat() seems to cause regressions for some load because
> the cpu going idle is a "fastpath". Mind boogling. Strange claim.
> If the system goes idle then it has nothing to do after all
>
> But anyways if we shift the quiet_vmstat() into the NOHZ logic
> when it stops the tick then it will only affect those cores that
> are setup for NOHZ mode. That is where we want this processing
> after all to ensure that the OS keeps itself off those cores.
>
> Signed-off-by: Christoph Lameter <c...@linux.com>
>
>
> Index: linux/kernel/sched/idle.c
> ===================================================================
> --- linux.orig/kernel/sched/idle.c
> +++ linux/kernel/sched/idle.c
> @@ -213,7 +213,6 @@ static void cpu_idle_loop(void)
> */
>
> __current_set_polling();
> - quiet_vmstat();
> tick_nohz_idle_enter();
>
> while (!need_resched()) {
> Index: linux/kernel/time/tick-sched.c
> ===================================================================
> --- linux.orig/kernel/time/tick-sched.c
> +++ linux/kernel/time/tick-sched.c
> @@ -811,6 +811,7 @@ static void __tick_nohz_idle_enter(struc
> ts->idle_calls++;
>
> expires = tick_nohz_stop_sched_tick(ts, now, cpu);
> + quiet_vmstat();
> if (expires.tv64 > 0LL) {
> ts->idle_sleeps++;
> ts->idle_expires = expires;
