On Fri, 17 Sep 2010 08:55:18 +0800, ykzhao wrote: > On Thu, 2010-09-16 at 15:16 +0800, Miao Xie wrote: >> 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, > > Where do you find that the "REP" instruction is not supported on some > CPUs? The comment in arch/x86/lib/memcpy_64.s only states that some CPUs > will run faster when using string copy instruction. Sorry! I misread the comment. >> 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(). > > Will you please look at tip/x86/ tree(mem branch)? The memory copy on > x86_64 is already optimized. Thanks for your reminding! It is very helpful. Miao > thanks. > Yakui >> >> Thanks! >> Miao >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
