Subject: Re: [Bugme-new] [Bug 12562] New: High overhead while switching or
 synchronizing threads on different cores
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Thomas Pilarski <thomas.pi@arcor.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mike Galbraith <efault@gmx.de>,
       Gregory Haskins <ghaskins@novell.com>, bugme-daemon@bugzilla.kernel.org,
       linux-kernel@vger.kernel.org
In-Reply-To: <1233181507.6988.14.camel@bugs-laptop>
References: <bug-12562-10286@http.bugzilla.kernel.org/>
	 <20090128125604.94ed3fe0.akpm@linux-foundation.org>
	 <1233181507.6988.14.camel@bugs-laptop>
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Date: Thu, 29 Jan 2009 10:07:28 +0100
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On Wed, 2009-01-28 at 23:25 +0100, Thomas Pilarski wrote:
> Am Mittwoch, den 28.01.2009, 12:56 -0800 schrieb Andrew Morton: 
> 
> > (There's testcase code in the bugzilla report)
> > 
> > (Seems to be a regression)
> 
> There is a regression, because of the improved cpu switching. The
> problem exists in every kernel. 

This is a contradiction in terms - twice.

If it is a regression, then clearly things haven't improved.

If it is a regression, state clearly when it worked last. If it never
worked, it cannot be a regression.

> I takes a lot of time to switch between the threads, when they are
> executed on different cores.
> Perhaps of the big buffer size of 512KB?

Of course, pushing 512kb to another cpu means lots and lots of cache
misses.

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