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" <users@ovirt.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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