From: Miao Xie <miaox@cn.fujitsu.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>, "Theodore Ts'o" <tytso@mit.edu>,
Chris Mason <chris.mason@oracle.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Linux Btrfs <linux-btrfs@vger.kernel.org>,
Linux Ext4 <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH] x86_64/lib: improve the performance of memmove
Date: Thu, 16 Sep 2010 15:16:31 +0800 [thread overview]
Message-ID: <4C91C44F.40700@cn.fujitsu.com> (raw)
In-Reply-To: <56957.91.60.149.91.1284619705.squirrel@www.firstfloor.org>
On Thu, 16 Sep 2010 08:48:25 +0200 (cest), Andi Kleen wrote:
>> When the dest and the src do overlap and the memory area is large, memmove
>> of
>> x86_64 is very inefficient, and it led to bad performance, such as btrfs's
>> file
>> deletion performance. This patch improved the performance of memmove on
>> x86_64
>> by using __memcpy_bwd() instead of byte copy when doing large memory area
>> copy
>> (len> 64).
>
>
> I still don't understand why you don't simply use a backwards
> string copy (with std) ? That should be much simpler and
> hopefully be as optimized for kernel copies on recent CPUs.
But according to the comment of memcpy, some CPUs don't support "REP" instruction,
so I think we must implement a backwards string copy by other method for those CPUs,
But that implement is complex, so I write it as a function -- __memcpy_bwd().
Thanks!
Miao
next prev parent reply other threads:[~2010-09-16 7:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-16 6:48 [PATCH] x86_64/lib: improve the performance of memmove Andi Kleen
2010-09-16 7:16 ` Miao Xie [this message]
2010-09-16 8:40 ` Andi Kleen
2010-09-16 9:29 ` Miao Xie
2010-09-16 10:11 ` Andi Kleen
2010-09-16 10:47 ` Miao Xie
2010-09-16 11:47 ` Miao Xie
2010-09-17 0:55 ` ykzhao
2010-09-17 3:37 ` Miao Xie
-- strict thread matches above, loose matches on Subject: below --
2010-09-16 12:13 George Spelvin
2010-09-16 6:31 Miao Xie
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