Dan Williams <[email protected]> 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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