From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Paul Turner <pjt@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@android.com>,
Joel Fernandes <joelaf@google.com>
Subject: Re: [PATCH v2 0/4] Utilization estimation (util_est) for FAIR tasks
Date: Wed, 13 Dec 2017 16:23:02 +0000 [thread overview]
Message-ID: <20171213162302.GC8264@e110439-lin> (raw)
In-Reply-To: <20171213160357.3se4vvyo5lqud2uo@hirez.programming.kicks-ass.net>
On 13-Dec 17:03, Peter Zijlstra wrote:
> On Tue, Dec 05, 2017 at 05:10:14PM +0000, Patrick Bellasi wrote:
> > With this feature enabled, the measured overhead is in the range of ~1%
> > on the same HW/SW test configuration.
>
> That's quite a lot; did you look where that comes from?
I've tracked it down to util_est_dequeue() introduced by PATCH 2/4,
mainly due to the EWMA udpate. Initially the running average was
implemented using the library function provided in:
include/linux/average.h::DECLARE_EWMA
but that solution generated even more overhead.
That's why we switched to an "inline custom" implementation.
Hackbench is quite stressful for that path and we have also few
branches which can play a role. One for example has been added to
avoid the EWMA if the rolling average is "close enough" to the
current PELT value.
All that considered, that's why I disable by default the sched_feat,
in which case we have 0 overheads... in !SCHED_DEBUG kernel the code
is actually removed by the compiler.
In mobile systems (i.e. non-hackbench scenarios) the additional
benefits on tasks placement and OPP selection is likely still worth
the overhead.
Do you think the idea to have a Kconfig to enabled this feature only
on systems which do not care about the possible overheads is a viable
solution?
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2017-12-13 16:23 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-05 17:10 [PATCH v2 0/4] Utilization estimation (util_est) for FAIR tasks Patrick Bellasi
2017-12-05 17:10 ` [PATCH v2 1/4] sched/fair: always used unsigned long for utilization Patrick Bellasi
2017-12-06 8:56 ` Vincent Guittot
2018-01-10 12:14 ` [tip:sched/core] sched/fair: Use 'unsigned long' for utilization, consistently tip-bot for Patrick Bellasi
2017-12-05 17:10 ` [PATCH v2 2/4] sched/fair: add util_est on top of PELT Patrick Bellasi
2017-12-13 16:05 ` Peter Zijlstra
2017-12-15 14:02 ` Patrick Bellasi
2017-12-15 14:07 ` Peter Zijlstra
2017-12-15 15:22 ` Patrick Bellasi
2017-12-13 16:16 ` Peter Zijlstra
2017-12-15 12:14 ` Patrick Bellasi
2017-12-15 12:53 ` Peter Zijlstra
2017-12-15 15:41 ` Patrick Bellasi
2017-12-20 8:57 ` Peter Zijlstra
2017-12-20 9:02 ` Peter Zijlstra
2017-12-13 16:19 ` Peter Zijlstra
2017-12-13 16:36 ` Patrick Bellasi
2017-12-13 17:03 ` Peter Zijlstra
2017-12-15 12:03 ` Patrick Bellasi
2017-12-15 12:58 ` Peter Zijlstra
2017-12-05 17:10 ` [PATCH v2 3/4] sched/fair: use util_est in LB and WU paths Patrick Bellasi
2017-12-05 17:10 ` [PATCH v2 4/4] sched/cpufreq_schedutil: use util_est for OPP selection Patrick Bellasi
2017-12-16 2:35 ` Rafael J. Wysocki
2017-12-18 10:48 ` Patrick Bellasi
2017-12-13 16:03 ` [PATCH v2 0/4] Utilization estimation (util_est) for FAIR tasks Peter Zijlstra
2017-12-13 16:23 ` Patrick Bellasi [this message]
2017-12-13 17:56 ` Mike Galbraith
2017-12-15 16:13 ` Patrick Bellasi
2017-12-15 20:23 ` Mike Galbraith
2017-12-16 6:37 ` Mike Galbraith
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20171213162302.GC8264@e110439-lin \
--to=patrick.bellasi@arm.com \
--cc=dietmar.eggemann@arm.com \
--cc=joelaf@google.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=morten.rasmussen@arm.com \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=rafael.j.wysocki@intel.com \
--cc=tkjos@android.com \
--cc=vincent.guittot@linaro.org \
--cc=viresh.kumar@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.