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Subject: Re: [patch] sched: yield debugging
From: Tim Chen <tim.c.chen@linux.intel.com>
Reply-To: tim.c.chen@linux.intel.com
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org
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	 <20070729173735.GA4041@elte.hu>
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Organization: Intel
Date: Mon, 30 Jul 2007 11:10:52 -0700
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On Sun, 2007-07-29 at 19:37 +0200, Ingo Molnar wrote:
> Tim,
> 
> * Tim Chen <tim.c.chen@linux.intel.com> wrote:
> 

> 
> Could you try the patch below? It does not change the default behavior 
> of yield but introduces 2 other yield strategies which you can activate 
> runtime (if CONFIG_SCHED_DEBUG=y) via:
> 
>   # default one:
>   echo 0 > /proc/sys/kernel/sched_yield_bug_workaround
> 
>   # always queues the current task next to the next task:
>   echo 1 > /proc/sys/kernel/sched_yield_bug_workaround
> 
>   # NOP:
>   echo 2 > /proc/sys/kernel/sched_yield_bug_workaround
> 
> does variant '1' improve Java's VolanoMark performance perhaps?
> 

Here's a summary of Volanomark performance numbers:
Variant 0 is 80% down from 2.6.22
Variant 1 is 20% down from 2.6.22  (this is indeed helped)
Variant 2 is 89% down from 2.6.22

> i'm also wondering, which JDK is this, and where does Java make use of 
> sys_sched_yield()? It's a voefully badly defined (and thus unreliable) 
> system call, IMO Java should stop using it ASAP and use a saner locking 
> model.

I am using a JRockit JDK.

Thanks.
Tim