linux-kernel - Re: regression introduced by - timers: fix itimer/many thread hang

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Message-Id: <1225984098.7803.4642.camel@twins>
Date:	Thu, 06 Nov 2008 16:08:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Frank Mayhar <fmayhar@...gle.com>,
	Doug Chapman <doug.chapman@...com>, mingo@...e.hu,
	roland@...hat.com, adobriyan@...il.com, akpm@...ux-foundation.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: regression introduced by - timers: fix itimer/many thread hang

On Thu, 2008-11-06 at 09:03 -0600, Christoph Lameter wrote:
> On Thu, 6 Nov 2008, Peter Zijlstra wrote:
> 
> > Also, you just introduced per-cpu allocations for each thread-group,
> > while Christoph is reworking the per-cpu allocator, with one unfortunate
> > side-effect - its going to have a limited size pool. Therefore this will
> > limit the number of thread-groups we can have.
> 
> Patches exist that implement a dynamically growable percpu pool (using
> virtual mappings though). If the cost of the additional complexity /
> overhead is justifiable then we can make the percpu pool dynamically
> extendable.

Right, but I don't think the patch under consideration will fly anyway,
doing a for_each_possible_cpu() loop on every tick on all cpus isn't
really healthy, even for moderate sized machines.
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