netdev - Re: [PATCH 0/6] fs: Scalability of sockets/pipes allocation/deallocation on SMP

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Date:	Thu, 27 Nov 2008 08:44:41 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 0/6] fs: Scalability of sockets/pipes allocation/deallocation
 on SMP

On Thu, 27 Nov 2008, Eric Dumazet wrote:

> with slub_min_objects=45 :
>
> # cat /sys/kernel/slab/filp/order
> 2
> # time ./socket8
> real    0m1.652s
> user    0m0.694s
> sys     0m12.367s

That may be a good value. How many processor do you have? Look at
calculate_order() in mm/slub.c:

   if (!min_objects)
                min_objects = 4 * (fls(nr_cpu_ids) + 1);

We couild increase the scaling factor there or start
with a mininum of 20 objects?


Try

	min_objects = 20 + 4 * (fls(nr_cpu_ids) + 1);

> I would say slub_min_objects=45 is the optimal value on 32bit arches to
> get acceptable performance on this workload (order=2 for filp kmem_cache)
>
> Note : SLAB here is disastrous, but you already knew that :)

Its good though to have examples where the queue management gets in the
way of performance.
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