linux-kernel - Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE

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Date:	Wed, 3 Jun 2015 16:34:01 -0400
From:	Josef Bacik <jbacik@...com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, <mingo@...hat.com>,
	<linux-kernel@...r.kernel.org>, <morten.rasmussen@....com>,
	kernel-team <Kernel-team@...com>
Subject: Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for
 BALANCE_WAKE

On 06/03/2015 01:43 PM, Mike Galbraith wrote:
> On Wed, 2015-06-03 at 13:16 -0400, Josef Bacik wrote:
>
>> Eesh ok, do you happen to remember how you ran tbench so I can add it to
>> my tests here?  In addition to fixing this problem we're also interested
>> in tracking performance of new kernels so we don't have to do this "what
>> the hell went wrong in the last 6 releases" dance every year, so I'm
>> throwing every performance thing we find useful in our test
>> infrastructure.  Thanks,
>>
>> Josef
>
> Start a tbench server, then tbench -t 30 1 localhost.  You're unlikely
> to find anything as painful as that bouncing cow bug was, but you won't
> have to look hard at all to find bounce pain.
>
> There are also other loads like your server where waking to an idle cpu
> dominates all else, pgbench is one of those.  In that case, you've got a
> 1:N waker/wakee relationship, and what matters above ALL else is when
> the mother of all work (the single server thread) wants a CPU, it had
> better get it NOW, else the load stalls.  Likewise, 'mom' being
> preempted hurts truckloads.  Perhaps your server has a similar thing
> going on, keeping wakees the hell away from the waker rules all.
>

Yeah our server has two waker threads (one per numa node) and then the N 
number of wakee threads.  I'll run tbench and pgbench with the new 
patches and see if there's a degredation.  Thanks,

Josef

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