Re: [Qemu-devel] [PATCH 0/7] qcow2: Reduce the number of I/O ops when doing COW

[Alberto Garcia]

On Wed 24 May 2017 06:26:23 PM CEST, Anton Nefedov wrote:
>>> I agree; as mentioned we have similar patches and they don't
>>> conflict much.  We noticed a performance regression on HDD though,
>>> for the presumably optimized case (random 4k write over a large
>>> backed image); so the patches were put on hold.
>> 
>> Interesting, I think that scenario was noticeably faster in my
>> tests. What cluster size(s) and image size(s) were you using?
>> 
> 64k cluster, 2g image, write 32m in portions of 4k at random offsets

I just tried that and the optimized case performs better (as expected),
almost twice as fast in fact:

write: io=32892KB, bw=162944B/s, iops=39, runt=206705msec
write: io=32892KB, bw=309256B/s, iops=75, runt=108911msec

I'll try in a different machine.

Berto