On Fri, Sep 18, 2020 at 10:59 AM Denis V. Lunev <[email protected]> wrote: > On 9/17/20 3:41 PM, Stefan Hajnoczi wrote: > > On Wed, Sep 16, 2020 at 5:43 PM Denis V. Lunev <[email protected]> wrote: > >> On 9/16/20 5:07 PM, Denis V. Lunev wrote: > >>> I will make a check today. > >>> > >>> Talking about our performance measurements, we have not > >>> seen ANY performance degradation, especially 30-40%. > >>> This looking quite strange to me. > >>> > >>> Though there is quite important difference. We are always > >>> using O_DIRECT and 'native' AIO engine. > >>> > >>> Den > >> I have put my hands into this and it looks like you are right. There is > >> a difference. It is not as significant for me as in your case, but I > >> observe > >> stable around 10% difference with 128 vs 256 queue size. > >> > >> I have checked with: > >> - QEMU 5.1 > >> - Fedora 31 in guest > >> - qcow2 (64k, 1Mb) and raw image on host > >> - nocache and both threaded/native IO modes > >> > >> The test was run on Thinkpad Carbon X1 gen 6 laptop. > >> > >> For the reference, I have seen 330k IOPS for read > >> at max which is looking awesome for native and 220k > >> IOPS for threads. > > Thanks for confirming! Reverting the commit is unattractive since it > > does improve performance in some cases. > > > > It would be good to understand the root cause so the regression can be > > fixed without reducing queue-size again. > > > > Do you have time to investigate? > I will make a try next week.
Thanks! Stefan
