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

From: Anton Nefedov
Subject: Re: [Qemu-block] [PATCH 0/7] qcow2: Reduce the number of I/O ops when doing COW
Date: Wed, 24 May 2017 19:09:42 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 05/24/2017 05:20 PM, Alberto Garcia wrote:
On Tue 23 May 2017 04:36:52 PM CEST, Eric Blake wrote:

here's a patch series that rewrites the copy-on-write code in the
qcow2 driver to reduce the number of I/O operations.

And it competes with Denis and Anton's patches:

What plan of attack should we take on merging the best parts of these
two series?

I took a look at that series and unless I overlooked something important
it seems that there's actually not that much overlap. Denis and Anton's
series deals with cluster preallocation and mine reduces the number of
I/O operations when there's a COW scenario. Most of my modifications are
in the peform_cow() function, but they barely touch that one.

I think we can review both separately, either of us can rebase our
series on top of the other, I don't expect big changes or conflicts.


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.
SSD looked fine though.


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