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

[Anton Nefedov]

On 05/26/2017 01:17 PM, Kevin Wolf wrote:
> Am 24.05.2017 um 18:09 hat Anton Nefedov geschrieben:
> > 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.
>
> You're talking about your own patches that should do the same thing,
> right? Can you re-do the same test with Berto's patches? Maybe there was
> just an implementation glitch in yours.
>
> This approach should very obviously result in a performance improvement,
> and the patches are relatively simple, so I'm very much inclined to
> merge this as soon as possible.
>
> Kevin


Tried the another machine; about 10% improvement here

address@hidden centos-7.3-x86_64]# qemu-img info ./harddisk2.hdd
image: ./harddisk2.hdd
file format: qcow2
virtual size: 2.0G (2147483648 bytes)
disk size: 260K
cluster_size: 65536
backing file: harddisk2.hdd.base (actual path: ./harddisk2.hdd.base)
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
address@hidden centos-7.3-x86_64]# qemu-img info ./harddisk2.hdd.base
image: ./harddisk2.hdd.base
file format: qcow2
virtual size: 2.0G (2147483648 bytes)
disk size: 2.0G
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: true
refcount bits: 16
corrupt: false
address@hidden centos-7.3-x86_64]# filefrag ./harddisk2.hdd.base
./harddisk2.hdd.base: 3 extents found


address@hidden ~]# fio --name=randwrite --blocksize=4k
--filename=/dev/sdb --rw=randwrite --direct=1 --ioengine=libaio
--size=2g --io_size=32m

/* master */
write: io=32768KB, bw=372785B/s, iops=91, runt= 90010msec
/* Berto's patches */
write: io=32768KB, bw=404304B/s, iops=98, runt= 82993msec


/Anton