Im in the middle of a priority issue right now, so cant take time out to rerun the bench, but... Usually in that kind of situation, if you dont turn on sync-to-disk on every write, you get benchmarks that are artificially HIGH. Forcing O_DIRECT slows throughput down. Dont you think the results are bad enough already? :-}
----- Original Message ----- From: "Stefan Hajnoczi" <[email protected]> To: "Philip Brown" <[email protected]> Cc: "Nir Soffer" <[email protected]>, "users" <[email protected]>, "qemu-block" <[email protected]>, "Paolo Bonzini" <[email protected]>, "Sergio Lopez Pascual" <[email protected]>, "Mordechai Lehrer" <[email protected]>, "Kevin Wolf" <[email protected]> Sent: Thursday, July 23, 2020 6:09:39 AM Subject: Re: [BULK] Re: [ovirt-users] very very bad iscsi performance Hi, At first glance it appears that the filebench OLTP workload does not use O_DIRECT, so this isn't a measurement of pure disk I/O performance: https://github.com/filebench/filebench/blob/master/workloads/oltp.f If you suspect that disk performance is the issue please run a benchmark that bypasses the page cache using O_DIRECT. The fio setting is direct=1. Here is an example fio job for 70% read/30% write 4KB random I/O: [global] filename=/path/to/device runtime=120 ioengine=libaio direct=1 ramp_time=10 # start measuring after warm-up time [read] readwrite=randrw rwmixread=70 rwmixwrite=30 iodepth=64 blocksize=4k (Based on https://blog.vmsplice.net/2017/11/common-disk-benchmarking-mistakes.html) Stefan _______________________________________________ Users mailing list -- [email protected] To unsubscribe send an email to [email protected] Privacy Statement: https://www.ovirt.org/privacy-policy.html oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/ List Archives: https://lists.ovirt.org/archives/list/[email protected]/message/5LCSEPHJP4GW6PAUN4ZUAJWEQUEJ6J7F/
