Subject: Re: regression introduced by - timers: fix itimer/many thread hang
From: Peter Zijlstra <peterz@infradead.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Frank Mayhar <fmayhar@google.com>, Doug Chapman <doug.chapman@hp.com>,
       mingo@elte.hu, roland@redhat.com, adobriyan@gmail.com,
       akpm@linux-foundation.org, linux-kernel <linux-kernel@vger.kernel.org>
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Date: Thu, 06 Nov 2008 16:08:18 +0100
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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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