From: Steve Muckle <steve.muckle@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
"Rafael J. Wysocki" <rafael@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <Juri.Lelli@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Michael Turquette <mturquette@baylibre.com>
Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()
Date: Wed, 30 Mar 2016 18:42:20 -0700 [thread overview]
Message-ID: <56FC807C.80204@linaro.org> (raw)
In-Reply-To: <20160330193544.GD407@worktop>
On 03/30/2016 12:35 PM, Peter Zijlstra wrote:
> On Mon, Mar 28, 2016 at 12:38:26PM -0700, Steve Muckle wrote:
>> Without covering all the paths where CFS utilization changes it's
>> possible to have to wait up to a tick to act on some changes, since the
>> tick is the only guaranteed regularly-occurring instance of the hook.
>> That's an unacceptable amount of latency IMO...
>
> Note that even with your patches that might still be the case. Remote
> wakeups might not happen on the destination CPU at all, so it might not
> be until the next tick (which always happens locally) that we'll
> 'observe' the utilization change brought with the wakeups.
>
> We could force all the remote wakeups to IPI the destination CPU, but
> that comes at a significant performance cost.
What about only IPI'ing the destination when the utilization change is
known to require a higher CPU frequency?
next prev parent reply other threads:[~2016-03-31 1:42 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-22 0:21 [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Steve Muckle
2016-03-22 0:21 ` [PATCH 2/2] sched/fair: do not call cpufreq hook unless util changed Steve Muckle
2016-03-24 23:47 ` Sai Gurrappadi
2016-03-25 1:01 ` Steve Muckle
2016-03-25 21:24 ` Sai Gurrappadi
2016-03-28 12:02 ` [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Dietmar Eggemann
2016-03-28 16:34 ` Steve Muckle
2016-03-28 18:30 ` Dietmar Eggemann
2016-03-28 19:38 ` Steve Muckle
2016-03-30 19:35 ` Peter Zijlstra
2016-03-31 1:42 ` Steve Muckle [this message]
2016-03-31 7:37 ` Peter Zijlstra
2016-03-31 21:26 ` Steve Muckle
2016-04-01 9:20 ` Peter Zijlstra
2016-04-11 19:28 ` Steve Muckle
2016-04-11 21:20 ` Rafael J. Wysocki
2016-04-12 14:29 ` Rafael J. Wysocki
2016-04-12 19:38 ` Steve Muckle
2016-04-13 14:45 ` Rafael J. Wysocki
2016-04-13 17:53 ` Steve Muckle
2016-04-13 19:39 ` Rafael J. Wysocki
2016-04-13 0:08 ` Steve Muckle
2016-04-13 4:48 ` Rafael J. Wysocki
2016-04-13 16:05 ` Rafael J. Wysocki
2016-04-13 16:07 ` Rafael J. Wysocki
2016-04-13 18:06 ` Steve Muckle
2016-04-13 19:50 ` Rafael J. Wysocki
2016-04-20 2:22 ` Steve Muckle
2016-03-31 9:27 ` Vincent Guittot
2016-03-31 9:34 ` Peter Zijlstra
2016-03-31 9:50 ` Vincent Guittot
2016-03-31 10:47 ` Peter Zijlstra
2016-03-31 12:14 ` Vincent Guittot
2016-03-31 12:34 ` Peter Zijlstra
2016-03-31 12:50 ` Vincent Guittot
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