Getting meaningful results is more important than getting good results. If the benchmark is not meaningful, it is not useful towards fixing the issue.
Did you try virtio-blk with direct LUN? Paolo Il gio 23 lug 2020, 16:35 Philip Brown <pbr...@medata.com> ha scritto: > 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" <stefa...@redhat.com> > To: "Philip Brown" <pbr...@medata.com> > Cc: "Nir Soffer" <nsof...@redhat.com>, "users" <firstname.lastname@example.org>, > "qemu-block" <qemu-bl...@nongnu.org>, "Paolo Bonzini" <pbonz...@redhat.com>, > "Sergio Lopez Pascual" <s...@redhat.com>, "Mordechai Lehrer" < > mleh...@redhat.com>, "Kevin Wolf" <kw...@redhat.com> > 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 > >
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