From: Vincent Guittot <vincent.guittot@linaro.org>
To: Rik van Riel <riel@surriel.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Kernel Team <kernel-team@fb.com>, Paul Turner <pjt@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load
Date: Wed, 28 Aug 2019 17:02:44 +0200 [thread overview]
Message-ID: <CAKfTPtBJb-f+LVLuQy4dbQrjGOiGzMe_3+wcwBiFgJttameCaQ@mail.gmail.com> (raw)
In-Reply-To: <98dffa226df25fd0d3017605bc7343c330f79a7e.camel@surriel.com>
On Wed, 28 Aug 2019 at 16:48, Rik van Riel <riel@surriel.com> wrote:
>
> On Wed, 2019-08-28 at 15:50 +0200, Vincent Guittot wrote:
> > Hi Rik,
> >
> > On Thu, 22 Aug 2019 at 04:18, Rik van Riel <riel@surriel.com> wrote:
> > > The runnable_load magic is used to quickly propagate information
> > > about
> > > runnable tasks up the hierarchy of runqueues. The runnable_load_avg
> > > is
> > > mostly used for the load balancing code, which only examines the
> > > value at
> > > the root cfs_rq.
> > >
> > > Redefine the root cfs_rq runnable_load_avg to be the sum of
> > > task_h_loads
> > > of the runnable tasks. This works because the hierarchical
> > > runnable_load of
> > > a task is already equal to the task_se_h_load today. This provides
> > > enough
> > > information to the load balancer.
> > >
> > > The runnable_load_avg of the cgroup cfs_rqs does not appear to be
> > > used for anything, so don't bother calculating those.
> > >
> > > This removes one of the things that the code currently traverses
> > > the
> > > cgroup hierarchy for, and getting rid of it brings us one step
> > > closer
> > > to a flat runqueue for the CPU controller.
> >
> > I like your proposal but just wanted to clarify one thing with this
> > patch.
> > Although you removed the computation of runnable_load_avg of the
> > cgroup cfs_rq, we are still traversing the hierarchy to update the
> > root cfs_rq runnable_load_avg because we are traversing the hierarchy
> > for computing the task_h_loads
>
> The task_h_load hierarchy traversal in update_cfs_rq_h_load
> is rate limited to once a jiffy, though. Rate limiting the
Ah yes. I forgot that it was jiffies and not clock_task that is used
for limiting the update
> hierarchy traversal significantly reduces overhead.
>
> > That being said, if we manage to remove the need on using
> > runnable_load_avg we will completely skip this traversal. I have a
> > proposal to remove it from load balance and wake up path but i
> > haven't
> > look at numa stats which also use it
>
> --
> All Rights Reversed.
next prev parent reply other threads:[~2019-08-28 15:03 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-22 2:17 [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Rik van Riel
2019-08-22 2:17 ` [PATCH 01/15] sched: introduce task_se_h_load helper Rik van Riel
2019-08-23 18:13 ` Dietmar Eggemann
2019-08-24 0:05 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 02/15] sched: change /proc/sched_debug fields Rik van Riel
2019-08-22 2:17 ` [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load Rik van Riel
2019-08-28 13:50 ` Vincent Guittot
2019-08-28 14:47 ` Rik van Riel
2019-08-28 15:02 ` Vincent Guittot [this message]
2019-08-22 2:17 ` [PATCH 04/15] sched,fair: move runnable_load_avg to cfs_rq Rik van Riel
2019-08-22 2:17 ` [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up Rik van Riel
2019-08-28 14:09 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 06/15] sched,cfs: use explicit cfs_rq of parent se helper Rik van Riel
2019-08-28 13:53 ` Vincent Guittot
2019-08-28 15:28 ` Rik van Riel
2019-08-28 16:34 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 07/15] sched,cfs: fix zero length timeslice calculation Rik van Riel
2019-08-28 16:59 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 08/15] sched,fair: simplify timeslice length code Rik van Riel
2019-08-28 17:32 ` Vincent Guittot
2019-08-28 23:18 ` Rik van Riel
2019-08-29 14:02 ` Vincent Guittot
2019-08-29 16:00 ` Rik van Riel
2019-08-30 6:41 ` Vincent Guittot
2019-08-30 15:01 ` Rik van Riel
2019-09-02 7:51 ` Vincent Guittot
2019-09-02 17:47 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 09/15] sched,fair: refactor enqueue/dequeue_entity Rik van Riel
2019-09-03 15:38 ` Vincent Guittot
2019-09-03 20:27 ` Rik van Riel
2019-09-04 6:44 ` Vincent Guittot
2019-08-22 2:17 ` [PATCH 10/15] sched,fair: add helper functions for flattened runqueue Rik van Riel
2019-08-22 2:17 ` [PATCH 11/15] sched,fair: flatten hierarchical runqueues Rik van Riel
2019-08-23 18:14 ` Dietmar Eggemann
2019-08-24 1:16 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 12/15] sched,fair: flatten update_curr functionality Rik van Riel
2019-08-27 10:37 ` Dietmar Eggemann
2019-08-22 2:17 ` [PATCH 13/15] sched,fair: propagate sum_exec_runtime up the hierarchy Rik van Riel
2019-08-28 7:51 ` Dietmar Eggemann
2019-08-28 13:14 ` Rik van Riel
2019-08-29 17:20 ` Dietmar Eggemann
2019-08-29 18:06 ` Rik van Riel
2019-08-22 2:17 ` [PATCH 14/15] sched,fair: ramp up task_se_h_weight quickly Rik van Riel
2019-08-22 2:17 ` [PATCH 15/15] sched,fair: scale vdiff in wakeup_preempt_entity Rik van Riel
2019-09-02 10:53 ` [PATCH RFC v4 0/15] sched,fair: flatten CPU controller runqueues Dietmar Eggemann
2019-09-03 1:44 ` Rik van Riel
2019-09-06 19:12 [PATCH RFC v5 " Rik van Riel
2019-09-06 19:12 ` [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load Rik van Riel
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