linux-kernel - Re: sched: tweak select_idle_sibling to look for idle threads

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Date:	Wed, 4 May 2016 13:46:16 -0400
From:	Chris Mason <clm@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Mike Galbraith <mgalbraith@...e.de>,
	Ingo Molnar <mingo@...nel.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	<linux-kernel@...r.kernel.org>
Subject: Re: sched: tweak select_idle_sibling to look for idle threads

On Wed, May 04, 2016 at 05:45:10PM +0200, Peter Zijlstra wrote:
> On Tue, May 03, 2016 at 11:11:53AM -0400, Chris Mason wrote:
> > # pick a single core, in my case cpus 0,20 are the same core
> > # cpu_hog is any program that spins
> > #
> > taskset -c 20 cpu_hog &
> > 
> > # schbench -p 4 means message passing mode with 4 byte messages (like
> > # pipe test), no sleeps, just bouncing as fast as it can.
> > #
> > # make the scheduler choose between the sibling of the hog and cpu 1
> > #
> > taskset -c 0,1 schbench -p 4 -m 1 -t 1
> 
> Will that schbench thingy print something? Mine doesn't seem to output
> anything, not actually exit, although it stops consuming CPU cycles at
> some point.
> 
> 

It should, make sure you're at the top commit in git.

git://git.kernel.org/pub/scm/linux/kernel/git/mason/schbench.git

It's not recent so I'd be surprised if you weren't already there.  The
default runtime is 30 seconds, but you can use -r to specify something
shorter.

It's possible I'm missing a wakeup to shut the whole thing down, but I
thought I fixed that.

 ./schbench -p 4 -m 1 -t 1
Latency percentiles (usec)
        50.0000th: 5
        75.0000th: 5
        90.0000th: 5
        95.0000th: 5
        *99.0000th: 8
        99.5000th: 15
        99.9000th: 17
        Over=0, min=0, max=652
avg worker transfer: 113768.27 ops/sec 444.41KB/s

-chris