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Re: [Qemu-block] [PATCH 0/7] qcow2: Reduce the number of I/O ops when do

From: Alberto Garcia
Subject: Re: [Qemu-block] [PATCH 0/7] qcow2: Reduce the number of I/O ops when doing COW
Date: Thu, 25 May 2017 13:48:39 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

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.


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