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.
Den
