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

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Message-ID: <1302158596.15889.7499.camel@debian>
Date:	Thu, 07 Apr 2011 14:43:16 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: [PATCH] sched: recover sched_yield task running time increase

On Thu, 2011-04-07 at 14:13 +0800, Rik van Riel wrote:
> On 04/06/2011 11:08 PM, Alex,Shi wrote:
> > On Wed, 2011-04-06 at 16:04 +0800, Peter Zijlstra wrote:
> >> On Wed, 2011-04-06 at 06:33 +0800, Alex Shi wrote:
> 
> >> 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.
> >
> > Yes, I used sched_compat_yield, otherwise volano will become extremely
> > slow in my single machine testing. We may reconsider our testing
> > setting.
> 
> With what JVM is this happening?

I used openjdk from fedora 10~13 and jrockit-R27.3.1-jre1.5.0_11, both
of them use sched_yield much. And I just did a quick try with
jrockit-R27.4.0-jre1.6.0_02.x86_64, it had same problem.

> 
> Surely not every JVM uses user space spinlocks and
> yield, when we have futexes available?

No, just 7 times futex called in testing, so I think the JVM did not use
it. 
> 
> 
> 


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