Re: [Qemu-devel] [PATCH v13 19/25] replay: add BH oneshot event for block layer

[Kevin Wolf]

Am 13.03.2019 um 06:57 hat Pavel Dovgalyuk geschrieben:
> Kevin, what about this one?

I made some benchmark on my system, too, and included some cases with
your series. I agree that there is no significant difference, so that's
fine.

Kevin

> > -----Original Message-----
> > From: Pavel Dovgalyuk [mailto:address@hidden
> > Sent: Wednesday, March 06, 2019 5:01 PM
> > To: 'Kevin Wolf'
> > Cc: 'Pavel Dovgalyuk'; address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden;
> > address@hidden; address@hidden
> > Subject: RE: [PATCH v13 19/25] replay: add BH oneshot event for block layer
> > 
> > > From: Kevin Wolf [mailto:address@hidden
> > > Am 06.03.2019 um 10:37 hat Pavel Dovgalyuk geschrieben:
> > > > > From: Kevin Wolf [mailto:address@hidden
> > > > > Am 06.03.2019 um 10:18 hat Pavel Dovgalyuk geschrieben:
> > > > > > > Something like:
> > > > > > >
> > > > > > > -drive file=null-co://,if=none,id=null -device 
> > > > > > > virtio-blk,drive=null
> > > > > >
> > > > > > And this drive should be destination of the copy operations, right?
> > > > >
> > > > > I don't know your exact benchmark, but this drive should be where the
> > > > > high I/O rates are, yes.
> > > >
> > > > Ok.
> > > >
> > > > > For getting meaningful numbers, you should have I/O only on the fast
> > > > > test disk (you're talking about a copy, where is source?),
> > > >
> > > > We used a qcow2 image as a source.
> > >
> > > So the source is going to slow down the I/O and you won't actually test
> > > whether the possible maximum changes.
> > >
> > > > > you should
> > > > > use direct I/O to get the page cache of the guest out of the way, and
> > > > > you should make sure that multiple requests are issued in parallel.
> > > >
> > > > Is this possible, if we have only conventional HDDs?
> > >
> > > null-co:// doesn't access your disk at all, so if this is the only
> > > virtual disk that has I/O, the conventional HDD doesn't hurt. But you're
> > > right that you probably can't use your physical disk for high
> > > performance benchmarks then.
> > >
> > > I'm going to suggest once more to use fio for storage testing. Actually,
> > > maybe I can find the time to do this myself on my system, too.
> > 
> > We've made some testing with the following fio configs:
> > 
> > [readtest]
> > blocksize=4k
> > filename=/dev/vda
> > rw=randread
> > direct=1
> > buffered=0
> > ioengine=libaio
> > iodepth=32
> > 
> > [writetest]
> > blocksize=4k
> > filename=/dev/vda
> > rw=randwrite
> > direct=1
> > buffered=0
> > ioengine=libaio
> > iodepth=32
> > 
> > One with read, one with write, and one with both.
> > 
> > master branch:
> > 1  read : io=1024.0MB, bw=475545KB/s, iops=118886, runt=  2205msec
> > 
> > 2  write: io=1024.0MB, bw=445444KB/s, iops=111361, runt=  2354msec
> > 
> > 3  read : io=1024.0MB, bw=229850KB/s, iops=57462, runt=  4562msec
> >    write: io=1024.0MB, bw=227210KB/s, iops=56802, runt=  4615msec
> > 
> > rr branch:
> > 1  read : io=1024.0MB, bw=479021KB/s, iops=119755, runt=  2189msec
> > 2  write: io=1024.0MB, bw=440763KB/s, iops=110190, runt=  2379msec
> > 
> > 3  read : io=1024.0MB, bw=230456KB/s, iops=57614, runt=  4550msec
> >    write: io=1024.0MB, bw=228548KB/s, iops=57136, runt=  4588msec
> > 
> > It seems that the difference can't be measured in our environment.
> > 
> > Pavel Dovgalyuk
> 
>