linux-kernel - Seemingly random performance degradation in 4.13

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Message-ID: <20170913042938.GY9731@shells.gnugeneration.com>
Date:   Tue, 12 Sep 2017 21:29:38 -0700
From:   vcaputo@...garu.com
To:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Seemingly random performance degradation in 4.13

Hello,

I've been working on some graphics hacks which has me paying close
attention to frame rates.  Something I've noticed recently in the 4.13
cycle is a seemingly random loss of ~40% frame rate.  These are purely
software-rendered hacks, and I haven't spent much time trying to figure out
what is changing when the performance drops - typically the performance is
restored on a subsequent boot.

There's been talk of NUMA and scheduler related performance regressions,
and I'm wondering if that's related to what I'm observing.

Is there a fix floating around I can apply and see if it prevents
regressions from occurring?

FYI the machine in question is a 1.8Ghz core2 duo thinkpad x61s, currently
on 4.13-rc7.

If there's anything in particular that would be useful for me to capture
when running one of these tests, a specific perf incantation for example,
I'm happy to test and report the results.

Cheers,
Vito Caputo