linux-kernel - Re: [PATCH] slub: reduce overhead of slub

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Message-ID: <m2box5cplq.fsf@firstfloor.org>
Date:	Thu, 07 Jul 2011 22:23:45 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	David Miller <davem@...emloft.net>, marcin.slusarz@...il.com,
	mpm@...enic.com, linux-kernel@...r.kernel.org, rientjes@...gle.com,
	linux-mm@...ck.org
Subject: Re: [PATCH] slub: reduce overhead of slub_debug

Christoph Lameter <cl@...ux.com> writes:


> +#ifdef __HAVE_ARCH_INV_MEMSCAN
> +void *inv_memscan(void *addr, int c, size_t size)
> +{
> +	if (!size)
> +		return addr;
> +	asm volatile("repz; scasb\n\t"

This will just do the slow byte accesses again internally.
scasb is not normally very optimized in microcode as far
as I know.

Also rep has quite some startup overhead which makes
it a bad idea for small sizes (<16-20 or so)

I would stay with the C version. I bet that one is 
faster.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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