linux-kernel - Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and SPECjvm2008 benchmarks against 4.6 kernel

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Message-ID: <20160623183318.GN30154@twins.programming.kicks-ass.net>
Date:	Thu, 23 Jun 2016 20:33:18 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jirka Hladky <jhladky@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Kamil Kolakowski <kkolakow@...hat.com>
Subject: Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and
 SPECjvm2008 benchmarks against 4.6 kernel

On Fri, Jun 17, 2016 at 01:04:23AM +0200, Jirka Hladky wrote:

> > What kind of config and userspace setup? Do you run this cruft in a
> > cgroup of sorts?
> 
>  No, we don't do any special setup except to control the number of threads.

OK, so I'm fairly certain you _do_ run in a cgroup, because its made
almost impossible not to these days.

Run:

	grep java /proc/sched_debug

while the thing is running. That'll show you the actual cgroup the stuff
is running in.

This modern Linux stuff stinks loads. And even Debian seems infected to
the point of almost being useless :-(

The _only_ reason I could reproduce was because I recently did an
upgrade of Debian Testing and I hadn't noticed just how messed up things
had become.

When I run it in the root cgroup (I had to kill cgmanager and reboot)
the numbers are just fine.

In any case, now I gotta go look at the cgroup code...