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To: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat
From: Andi Kleen <andi@firstfloor.org>
References: <20090701.152115.706994265076015808.mitake@dcl.info.waseda.ac.jp>
Date: Wed, 01 Jul 2009 09:38:04 +0200
In-Reply-To: <20090701.152115.706994265076015808.mitake@dcl.info.waseda.ac.jp> (Hitoshi Mitake's message of "Wed, 01 Jul 2009 15:21:15 +0900 (JST)")
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Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp> writes:

> Hi,
>
> I wrote a test patch which add information of counts processes acquired how many spinlocks to schedstat.
> After applied this patch, /proc/<PID>/sched will change like this,

The problem is that spinlocks are very common and schedstats is enabled commonly
in production kernels. You would need to demonstrate that such a change doesn't
have significant performance impact. For me it looks like it has.

Also I'm not sure exactly what good such a metric is. Do you have 
a concrete use case?

The normal way to check for lock contention or lock bouncingis to
simply profile cycles or time and see if there is a lot of CPU time in
locks.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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