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Message-ID: <4C91C44F.40700@cn.fujitsu.com> Date: Thu, 16 Sep 2010 15:16:31 +0800 From: Miao Xie <miaox@...fujitsu.com> To: Andi Kleen <andi@...stfloor.org> CC: Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...e.hu>, "Theodore Ts'o" <tytso@....edu>, Chris Mason <chris.mason@...cle.com>, Linux Kernel <linux-kernel@...r.kernel.org>, Linux Btrfs <linux-btrfs@...r.kernel.org>, Linux Ext4 <linux-ext4@...r.kernel.org> Subject: Re: [PATCH] x86_64/lib: improve the performance of memmove 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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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