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From: Andi Kleen <andi@firstfloor.org>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>,
	David Miller <davem@davemloft.net>,
	marcin.slusarz@gmail.com, mpm@selenic.com,
	linux-kernel@vger.kernel.org, rientjes@google.com,
	linux-mm@kvack.org
Subject: Re: [PATCH] slub: reduce overhead of slub_debug
Date: Thu, 07 Jul 2011 22:23:45 -0700	[thread overview]
Message-ID: <m2box5cplq.fsf@firstfloor.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1107071511010.26083@router.home> (Christoph Lameter's message of "Thu, 7 Jul 2011 15:12:52 -0500 (CDT)")

Christoph Lameter <cl@linux.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@linux.intel.com -- Speaking for myself only

WARNING: multiple messages have this Message-ID (diff)
From: Andi Kleen <andi@firstfloor.org>
To: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>,
	David Miller <davem@davemloft.net>,
	marcin.slusarz@gmail.com, mpm@selenic.com,
	linux-kernel@vger.kernel.org, rientjes@google.com,
	linux-mm@kvack.org
Subject: Re: [PATCH] slub: reduce overhead of slub_debug
Date: Thu, 07 Jul 2011 22:23:45 -0700	[thread overview]
Message-ID: <m2box5cplq.fsf@firstfloor.org> (raw)
In-Reply-To: <alpine.DEB.2.00.1107071511010.26083@router.home> (Christoph Lameter's message of "Thu, 7 Jul 2011 15:12:52 -0500 (CDT)")

Christoph Lameter <cl@linux.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@linux.intel.com -- Speaking for myself only

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  reply	other threads:[~2011-07-08  5:25 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-26 19:39 [PATCH] slub: reduce overhead of slub_debug Marcin Slusarz
2011-06-26 19:39 ` Marcin Slusarz
2011-06-28 19:32 ` Christoph Lameter
2011-06-28 19:32   ` Christoph Lameter
2011-06-28 19:40   ` David Daney
2011-06-28 19:40     ` David Daney
2011-06-28 20:58     ` David Rientjes
2011-06-28 20:58       ` David Rientjes
2011-06-28 21:04       ` Ben Greear
2011-06-28 21:04         ` Ben Greear
2011-06-28 21:10         ` David Rientjes
2011-06-28 21:10           ` David Rientjes
2011-06-28 21:16       ` Dave Jones
2011-06-28 21:16         ` Dave Jones
2011-07-07 18:07 ` Pekka Enberg
2011-07-07 18:07   ` Pekka Enberg
2011-07-07 18:17   ` Christoph Lameter
2011-07-07 18:17     ` Christoph Lameter
2011-07-07 18:30     ` Ben Greear
2011-07-07 18:30       ` Ben Greear
2011-07-07 18:42       ` Christoph Lameter
2011-07-07 18:42         ` Christoph Lameter
2011-07-07 18:54         ` Ben Greear
2011-07-07 18:54           ` Ben Greear
2011-07-07 18:30     ` Matt Mackall
2011-07-07 18:30       ` Matt Mackall
2011-07-07 18:52     ` Pekka Enberg
2011-07-07 18:52       ` Pekka Enberg
2011-07-07 18:55       ` Matt Mackall
2011-07-07 18:55         ` Matt Mackall
2011-07-07 19:12       ` Christoph Lameter
2011-07-07 19:12         ` Christoph Lameter
2011-07-07 19:21         ` David Miller
2011-07-07 19:21           ` David Miller
2011-07-07 19:49           ` Pekka Enberg
2011-07-07 19:49             ` Pekka Enberg
2011-07-07 20:12             ` Christoph Lameter
2011-07-07 20:12               ` Christoph Lameter
2011-07-08  5:23               ` Andi Kleen [this message]
2011-07-08  5:23                 ` Andi Kleen
2011-07-08 17:41                 ` Christoph Lameter
2011-07-08 17:41                   ` Christoph Lameter
2011-07-08  5:38               ` Pekka Enberg
2011-07-08  5:38                 ` Pekka Enberg

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