linux-kernel - Re: [Bugme-new] [Bug 12562] New: High overhead while switching or synchronizing threads on different cores

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Message-Id: <1233220048.7835.19.camel@twins>
Date:	Thu, 29 Jan 2009 10:07:28 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Thomas Pilarski <thomas.pi@...or.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Gregory Haskins <ghaskins@...ell.com>,
	bugme-daemon@...zilla.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Bugme-new] [Bug 12562] New: High overhead while switching or
 synchronizing threads on different cores

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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