Message-ID: <1448966661.3225.141.camel@gmail.com>
Subject: Re: [RFC PATCH 3/3] sched/fair: Use different cachelines for
 readers and writers of load_avg
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <waiman.long@hpe.com>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>, Paul Turner <pjt@google.com>,
        Ben Segall <bsegall@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Yuyang Du <yuyang.du@intel.com>
Date: Tue, 01 Dec 2015 11:44:21 +0100
In-Reply-To: <20151201084944.GK3816@twins.programming.kicks-ass.net>
References: <1448478580-26467-1-git-send-email-Waiman.Long@hpe.com>
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	 <20151130102240.GH17308@twins.programming.kicks-ass.net>
	 <565C9FDC.9020603@hpe.com>
	 <20151130220953.GD3816@twins.programming.kicks-ass.net>
	 <565D1A16.7080105@hpe.com>
	 <20151201084944.GK3816@twins.programming.kicks-ass.net>
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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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