From: Peter Zijlstra <peterz@infradead.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Mike Galbraith <mgalbraith@suse.de>,
mingo@redhat.com, dietmar.eggemann@arm.com, yuyang.du@intel.com,
vincent.guittot@linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide
Date: Thu, 2 Jun 2016 10:05:09 +0200 [thread overview]
Message-ID: <20160602080509.GU3205@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160601195723.GD28447@twins.programming.kicks-ass.net>
On Wed, Jun 01, 2016 at 09:57:23PM +0200, Peter Zijlstra wrote:
> On Mon, May 23, 2016 at 01:00:10PM +0100, Morten Rasmussen wrote:
> > On Mon, May 23, 2016 at 01:12:07PM +0200, Mike Galbraith wrote:
> > > On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen wrote:
> > > > wake_wide() is based on task wakee_flips of the waker and the wakee to
> > > > decide whether an affine wakeup is desirable. On lightly loaded systems
> > > > the waker is frequently the idle task (pid=0) which can accumulate a lot
> > > > of wakee_flips in that scenario. It makes little sense to prevent affine
> > > > wakeups on an idle cpu due to the idle task wakee_flips, so it makes
> > > > more sense to ignore them in wake_wide().
> > >
> > > You sure? What's the difference between a task flipping enough to
> > > warrant spreading the load, and an interrupt source doing the same?
> > > I've both witnessed firsthand, and received user confirmation of this
> > > very thing improving utilization.
> >
> > Right, I didn't consider the interrupt source scenario, my fault.
> >
> > The problem then seems to be distinguishing truly idle and busy doing
> > interrupts. The issue that I observe is that wake_wide() likes pushing
> > tasks around in lightly scenarios which isn't desirable for power
> > management. Selecting the same cpu again may potentially let others
> > reach deeper C-state.
> >
> > With that in mind I will if I can do better. Suggestions are welcome :-)
>
> Seeing how we always so select_idle_siblings() after affine_sd, the only
> wake_affine movement that matters is cross-llc.
>
> So intra-llc wakeups can avoid the movement, no?
Won't help I think; the interrupt that got us in this situation will
already have wrecked your idle time/state to begin with. You really want
to help interrupt routing.
next prev parent reply other threads:[~2016-06-02 8:05 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-23 10:58 [PATCH 00/16] sched: Clean-ups and asymmetric cpu capacity support Morten Rasmussen
2016-05-23 10:58 ` [PATCH 01/16] sched: Fix power to capacity renaming in comment Morten Rasmussen
2016-05-23 10:58 ` [PATCH 02/16] sched/fair: Consistent use of prev_cpu in wakeup path Morten Rasmussen
2016-06-01 19:49 ` Peter Zijlstra
2016-05-23 10:58 ` [PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide Morten Rasmussen
2016-05-23 11:12 ` Mike Galbraith
2016-05-23 12:00 ` Morten Rasmussen
2016-05-23 13:00 ` Mike Galbraith
2016-05-23 14:10 ` Morten Rasmussen
2016-05-23 15:42 ` Mike Galbraith
2016-05-23 23:17 ` Yuyang Du
2016-05-23 23:04 ` Yuyang Du
2016-06-01 19:57 ` Peter Zijlstra
2016-06-02 8:05 ` Peter Zijlstra [this message]
2016-06-07 12:08 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 04/16] sched/fair: Optimize find_idlest_cpu() when there is no choice Morten Rasmussen
2016-05-24 6:29 ` Mike Galbraith
2016-05-24 8:05 ` Morten Rasmussen
2016-05-24 8:12 ` Mike Galbraith
2016-06-01 19:59 ` Peter Zijlstra
2016-06-07 14:25 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 05/16] sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag Morten Rasmussen
2016-05-23 10:58 ` [PATCH 06/16] sched: Disable WAKE_AFFINE for asymmetric configurations Morten Rasmussen
2016-05-24 9:10 ` Vincent Guittot
2016-05-24 10:29 ` Morten Rasmussen
2016-05-24 12:12 ` Vincent Guittot
2016-05-24 13:16 ` Morten Rasmussen
2016-05-24 13:27 ` Vincent Guittot
2016-05-24 13:36 ` Morten Rasmussen
2016-05-24 13:52 ` Vincent Guittot
2016-05-24 15:02 ` Morten Rasmussen
2016-05-24 15:53 ` Vincent Guittot
2016-05-25 9:12 ` Morten Rasmussen
2016-05-26 6:45 ` Vincent Guittot
2016-06-07 16:50 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 07/16] sched: Make SD_BALANCE_WAKE a topology flag Morten Rasmussen
2016-05-24 23:52 ` Yuyang Du
2016-05-25 9:27 ` Morten Rasmussen
2016-06-01 20:18 ` Peter Zijlstra
2016-06-08 8:45 ` Morten Rasmussen
2016-05-23 10:58 ` [PATCH 08/16] sched: Store maximum per-cpu capacity in root domain Morten Rasmussen
2016-05-23 10:58 ` [PATCH 09/16] sched/fair: Let asymmetric cpu configurations balance at wake-up Morten Rasmussen
2016-05-24 0:04 ` Yuyang Du
2016-05-24 8:10 ` Morten Rasmussen
2016-05-24 7:03 ` Mike Galbraith
2016-05-24 7:15 ` Mike Galbraith
2016-05-25 6:57 ` Wanpeng Li
2016-05-25 9:49 ` Morten Rasmussen
2016-05-25 10:29 ` Wanpeng Li
2016-05-25 10:54 ` Morten Rasmussen
2016-05-25 11:18 ` Wanpeng Li
2016-06-02 14:21 ` Peter Zijlstra
2016-06-08 11:29 ` Morten Rasmussen
2016-06-08 14:36 ` Peter Zijlstra
2016-05-23 10:58 ` [PATCH 10/16] sched/fair: Compute task/cpu utilization at wake-up more correctly Morten Rasmussen
2016-05-23 10:58 ` [PATCH 11/16] sched/fair: Consider spare capacity in find_idlest_group() Morten Rasmussen
2016-05-23 10:58 ` [PATCH 12/16] sched: Add per-cpu max capacity to sched_group_capacity Morten Rasmussen
2016-05-23 10:58 ` [PATCH 13/16] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Morten Rasmussen
2016-05-23 10:58 ` [PATCH 14/16] arm: Set SD_ASYM_CPUCAPACITY for big.LITTLE platforms Morten Rasmussen
2016-05-23 10:58 ` [PATCH 15/16] arm: Set SD_BALANCE_WAKE flag for asymmetric capacity systems Morten Rasmussen
2016-05-23 10:58 ` [PATCH 16/16] arm: Update arch_scale_cpu_capacity() to reflect change to define Morten Rasmussen
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