Messages in this thread | | | Subject | Re: [RFC PATCH 0/2] raid5: 65% sequential-write performance improvement, stripe-queue take2 | From | Andi Kleen <> | Date | 04 Jul 2007 13:41:26 +0200 |
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Dan Williams <dan.j.williams@intel.com> writes:
> The write performance numbers are better than I expected and would seem > to address the concerns raised in the thread "Odd (slow) RAID > performance"[2]. The read performance drop was not expected. However, > the numbers suggest some additional changes to be made to the queuing > model.
Have you considered supporting copy-xor in MD for non accelerated RAID? I've been looking at fixing the old dubious slow crufty x86 SSE XOR functions. One thing I discovered is that it seems fairly pointless to make them slower with cache avoidance when most of the data is copied before anyways. I think much more advantage could be gotten by supporting copy-xor because XORing during a copy should be nearly free.
On the other hand ext3 write() also uses a cache avoiding copy now and for the XOR it would need to load the data from memory again. Perhaps this could be also optimized somehow (e.g. setting a flag somewhere and using a normal copy for the RAID-5 case)
-Andi
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