linux-kernel - Re: [RFC][PATCH 00/13] percpu rwsem -v2

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Message-ID: <20150624090142.GJ3644@twins.programming.kicks-ass.net>
Date:	Wed, 24 Jun 2015 11:01:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Daniel Wagner <daniel.wagner@...-carit.de>, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, tj@...nel.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org, der.herr@...r.at, dave@...olabs.net,
	riel@...hat.com, viro@...IV.linux.org.uk,
	torvalds@...ux-foundation.org, jlayton@...chiereds.net
Subject: Re: [RFC][PATCH 00/13] percpu rwsem -v2

On Wed, Jun 24, 2015 at 10:46:48AM +0200, Ingo Molnar wrote:
> > > > flock02
> > > >                              mean   variance      sigma        max        min
> > > >                     tip-1    11.8994     0.5874     0.7664    13.2022     8.6324
> > > >                     tip-2    11.7394     0.5252     0.7247    13.2540     9.7513
> > > >                     tip-3    11.8155     0.5288     0.7272    13.2700     9.9480
> > > >        tip+percpu-rswem-1    15.3601     0.8981     0.9477    16.8116    12.6910
> > > >        tip+percpu-rswem-2    15.2558     0.8442     0.9188    17.0199    12.9586
> > > >        tip+percpu-rswem-3    15.5297     0.6386     0.7991    17.4392    12.7992

> [ Such high variance is often caused by (dynamically) unstable load balancing and 
>   the workload never finding a good equilibrium. Any observable locking overhead 
>   is usually just a second order concern or a symptom. Assuming the workload 
>   context switches heavily. ]

flock02 is a relatively stable benchmark -- unlike some of the others
where the variance is orders of magnitude higher than the avg.

But yes, I'll go poke at it more. I just need to hunt down unrelated
fail before continuing with this.
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