linux-kernel - Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for readers and writers of load

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Date:	Tue, 01 Dec 2015 11:44:21 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Waiman Long <waiman.long@....com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Yuyang Du <yuyang.du@...el.com>
Subject: Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for
 readers and writers of load_avg

On Tue, 2015-12-01 at 09:49 +0100, Peter Zijlstra wrote:
> On Mon, Nov 30, 2015 at 10:55:02PM -0500, Waiman Long wrote:
> > On 11/30/2015 05:09 PM, Peter Zijlstra wrote:
> > >On Mon, Nov 30, 2015 at 02:13:32PM -0500, Waiman Long wrote:
> > >>>This begs the question tough; why are you running a global load in a
> > >>>cgroup; and do we really need to update this for the root cgroup? It
> > >>>seems to me we don't need calc_tg_weight() for the root cgroup, it
> > >>>doesn't need to normalize its weight numbers.
> > >>>
> > >>>That is; isn't this simply a problem we should avoid?
> > >>I didn't use any cgroup in my test setup. Autogroup was enabled, though.
> > >>Booting up a 4.4-rc2 kernel caused sched_create_group() to be called 56
> > >>times.
> > >Yeah, can you kill autogroup and see if that helps? If not, we probably
> > >should add some code to avoid calculating things for the root group.
> > 
> > I will try that out tomorrow. However, SCHED_AUTOGROUP was enabled in the
> > distribution kernels. So we still need to look at that with autogroup
> > enabled.
> 
> Meh, or just tell the people that have stupid large machines to use
> noautogroup on boot (its of questionable benefit in the first place imo,
> esp. on servers).

Yup (and yup).  Someone should also suggest to the systemd(isease) folks
that they try actually measuring before turning everything in the world
on.  "Oo cgroups are cool" is NOT a good reason to turn it all on :)

	-Mike

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