From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Qais Yousef <qais.yousef@arm.com>
Subject: Re: [PATCH 0/7 v4] move update blocked load outside newidle_balance
Date: Wed, 24 Feb 2021 18:41:09 +0100 [thread overview]
Message-ID: <YDaPtc47NnB5BGEW@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtCwmt9HHDuN7tVhZiy7R3e5XHuExU-PVOb++40fYzu-2Q@mail.gmail.com>
On Wed, Feb 24, 2021 at 04:57:15PM +0100, Vincent Guittot wrote:
> On Wed, 24 Feb 2021 at 16:54, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Wed, Feb 24, 2021 at 02:30:00PM +0100, Vincent Guittot wrote:
> > > Joel reported long preempt and irq off sequence in newidle_balance because
> > > of a large number of CPU cgroups in use and having to be updated. This
> > > patchset moves the update outside newidle_imblance. This enables to early
> > > abort during the updates in case of pending irq as an example.
> > >
> > > Instead of kicking a normal ILB that will wakes up CPU which is already
> > > idle, patch 6 triggers the update of statistics in the idle thread of
> > > the CPU before selecting and entering an idle state.
> >
> > I'm confused... update_blocked_averages(), which calls
> > __update_blocked_fair(), which is the one doing the cgroup iteration
> > thing, runs with rq->lock held, and thus will have IRQs disabled any
> > which way around we turn this thing.
> >
> > Or is the problem that we called nohz_idle_balance(), which does
> > update_nohz_stats() -> update_blocked_averages() for evey NOHZ cpu from
> > newidle balance, such that we get NR_NOHZ_CPUS * NR_CGROUPS IRQ latency?
> > Which is now reduced to just NR_CGROUPS ?
>
> Yes we can now abort between each cpu update
OK, shall I add something like:
This reduces the IRQ latency from O(nr_cgroups * nr_nohz_cpus) to
O(nr_cgroups).
To the changelog of patch #1 ?
next prev parent reply other threads:[~2021-02-24 17:42 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-24 13:30 [PATCH 0/7 v4] move update blocked load outside newidle_balance Vincent Guittot
2021-02-24 13:30 ` [PATCH 1/7 v4] sched/fair: remove update of blocked load from newidle_balance Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-06 11:42 ` tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 2/7 v4] sched/fair: remove unused return of _nohz_idle_balance Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-06 11:42 ` tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 3/7 v4] sched/fair: remove unused parameter of update_nohz_stats Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-05 13:55 ` [PATCH 3/7 v4] sched/fair: remove " Qais Yousef
2021-03-06 11:42 ` [tip: sched/core] sched/fair: Remove " tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 4/7 v4] sched/fair: merge for each idle cpu loop of ILB Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Merge " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-06 11:42 ` tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 5/7 v4] sched/fair: reorder newidle_balance pulled_task tests Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Reorder " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-06 11:42 ` tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 6/7 v4] sched/fair: trigger the update of blocked load on newly idle cpu Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Trigger " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-05 13:52 ` [PATCH 6/7 v4] sched/fair: trigger " Qais Yousef
2021-03-06 11:42 ` [tip: sched/core] sched/fair: Trigger " tip-bot2 for Vincent Guittot
2021-02-24 13:30 ` [PATCH 7/7 v4] sched/fair: reduce the window for duplicated update Vincent Guittot
2021-03-02 9:01 ` [tip: sched/core] sched/fair: Reduce " tip-bot2 for Vincent Guittot
2021-03-03 9:49 ` tip-bot2 for Vincent Guittot
2021-03-06 11:42 ` tip-bot2 for Vincent Guittot
2021-02-24 15:53 ` [PATCH 0/7 v4] move update blocked load outside newidle_balance Peter Zijlstra
2021-02-24 15:57 ` Vincent Guittot
2021-02-24 17:41 ` Peter Zijlstra [this message]
2021-02-24 17:51 ` Vincent Guittot
2021-02-24 18:17 ` Peter Zijlstra
2021-02-24 18:46 ` Valentin Schneider
2021-02-25 8:05 ` Vincent Guittot
2021-02-25 12:14 ` Valentin Schneider
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