linux-kernel - Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush

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Date:	Mon, 26 Sep 2011 13:03:19 +0300 (EEST)
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Chris Metcalf <cmetcalf@...era.com>, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 5/5] slub: Only IPI CPUs that have per cpu obj to flush

On Mon, 26 Sep 2011, Gilad Ben-Yossef wrote:
> Peter basically already answered better then I could :-)
>
> All I have to add is an example -
>
> flush_all() is called for each kmem_cahce_destroy(). So every cache
> being destroyed dynamically ends up sending an IPI to each CPU in the
> system, regardless if the cache has ever been used there.
>
> For example, if you close the Infinband ipath driver char device file,
> the close file ops calls kmem_cache_destroy().So, if I understand
> correctly, running some infiniband config tool on one a single CPU
> dedicated to system tasks might interrupt the rest of the 127 CPUs I
> dedicated to some CPU intensive task. This is the scenario I'm
> tryingto avoid.
>
> I suspect there is a good chance that every line in the output of "git
> grep kmem_cache_destroy linux/ | grep '\->'" has a similar scenario
> (there are 42 of them).
>
> I hope this sheds some light on the motive of the work.

Sure.

If you write down such information in the changelog for future patches, I 
don't need to waste your time asking for an explanation. ;-)

 			Pekka
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