From: Yuyang Du <yuyang.du@intel.com>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Mike Galbraith <mgalbraith@suse.de>,
peterz@infradead.org, mingo@redhat.com, dietmar.eggemann@arm.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: Tue, 24 May 2016 07:04:26 +0800 [thread overview]
Message-ID: <20160523230426.GD18670@intel.com> (raw)
In-Reply-To: <20160523120010.GB27946@e105550-lin.cambridge.arm.com>
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 :-)
On mobile, the factor is as small as 2 to 4, may easily be exceeded,
so decay at HZ may be too slow.
> >
> > > cc: Ingo Molnar <mingo@redhat.com>
> > > cc: Peter Zijlstra <peterz@infradead.org>
> > >
> > > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> > > ---
> > > kernel/sched/fair.c | 4 ++++
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index c49e25a..0fe3020 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -5007,6 +5007,10 @@ static int wake_wide(struct task_struct *p)
> > > unsigned int slave = p->wakee_flips;
> > > int factor = this_cpu_read(sd_llc_size);
> > >
> > > + /* Don't let the idle task prevent affine wakeups */
> > > + if (is_idle_task(current))
> > > + return 0;
> > > +
> > > if (master < slave)
> > > swap(master, slave);
> > > if (slave < factor || master < slave * factor)
next prev parent reply other threads:[~2016-05-24 7:02 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 [this message]
2016-06-01 19:57 ` Peter Zijlstra
2016-06-02 8:05 ` Peter Zijlstra
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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