linux-kernel - Re: [PATCH 3/5] slab.c: remove branch hint

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Date:	Wed, 25 Nov 2009 12:41:57 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Tim Blechmann <tim@...ngt.org>, linux-kernel@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 3/5] slab.c: remove branch hint

Ingo Molnar kirjoitti:
>> That sounds odd to me. Can you see where the incorrectly predicted
>> calls are coming from? Calling kmem_cache_alloc_node() with node set
>> to -1 most of the time could be a real bug somewhere.
> 
> I think it could occur in too limited tests - the branch prediction 
> looks 'wrong' in certain tests - while it's OK in general.
> 
> Is there some easy to run workload you consider more or less 
> representative of typical SLAB patterns?

I can think of three main classes: VFS, SCSI, or network intensive 
applications and benchmarks tend to bring out the worst in SLAB. There 
are probably some interesting NUMA related things that I'm not really 
aware of.
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