linux-kernel - Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived threads

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Message-Id: <1202790635.4165.43.camel@homer.simson.net>
Date:	Tue, 12 Feb 2008 05:30:35 +0100
From:	Mike Galbraith <efault@....de>
To:	Bill Davidsen <davidsen@....com>
Cc:	Olof Johansson <olof@...om.net>, Willy Tarreau <w@....eu>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived
	threads


On Mon, 2008-02-11 at 16:45 -0500, Bill Davidsen wrote:

> I think the moving to another CPU gets really dependent on the CPU type. 
> On a P4+HT the caches are shared, and moving costs almost nothing for 
> cache hits, while on CPUs which have other cache layouts the migration 
> cost is higher. Obviously multi-core should be cheaper than 
> multi-socket, by avoiding using the system memory bus, but it still can 
> get ugly.
> 
> I have an IPC test around which showed that, it ran like hell on HT, and 
> progressively worse as cache because less shared. I wonder why the 
> latest git works so much better?

Yes, I'm wondering the same.  With latest git, ~400 usec work units
suffice to achieve overlap (on my P4/HT), whereas all other kernels
tested require several milliseconds.

	-Mike

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