linux-kernel - Re: [PATCH] sched: recover sched_yield task running time increase

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Message-ID: <4D9C7BE1.6010502@redhat.com>
Date:	Wed, 06 Apr 2011 10:42:41 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Alex Shi <alex.shi@...el.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, tim.c.chen@...el.com, shaohua.li@...el.com
Subject: Re: [PATCH] sched: recover sched_yield task running time increase

On 04/06/2011 04:04 AM, Peter Zijlstra wrote:
> On Wed, 2011-04-06 at 06:33 +0800, Alex Shi wrote:
>> commit ac53db596cc08ecb8040c removed the sched_yield task running
>> time increase, so the yielded task get more opportunity to be launch
>> again. That may not the caller want to be. And this also causes
>> volano benchmark drop 50~80 percent performance on core2/NHM/WSM
>> machines. This patch recover the sched_yield task vruntime up.
>
> You do know that any app that relies on sched_yield behaviour is more
> than broken? Using sched_yield() for anything other than SCHED_FIFO
> tasks is well outside spec.
>
> Furthermore, apparently you used sysctl_sched_compat_yield, which was
> bound to disappear some time, since with the default settings the yield
> semantics didn't actually change.
>
> So no, I'm not much inclined to accept this. The Java people have had
> every opportunity to go fix their crap, them not doing so will
> eventually (preferably now) stop being my problem.

It appears they might not have figured out how to fix
their stuff :)

Would you have any hints on what the Java folks should
replace their calls to sched_yield with?

Proper use of futexes from inside the JVM perhaps?

Or should we export yield_to to userspace and have
them use that? :)   *runs*
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