[Virtio-fs] [QUESTION] A performance problem for buffer write compared with 9p

[Miklos Szeredi]

On Sat, Aug 24, 2019 at 10:44 AM wangyan <wangyan122 at huawei.com> wrote:

> According to the result, for "-size=1G", it maybe exceed the dirty pages'
> upper limit, and it frequently triggered pdflush for write-back. And for
> "-size=700M", it maybe didn't exceed the dirty pages' upper limit, so no
> extra pdflush was triggered.
>
> But for 9p using "-size=1G", the latency 3.94 usec, and the bandwidth is
> 2305.5MB/s. It is better than virtiofs using "-size=1G". It seems that
> it is not affected by the dirty pages' upper limit.

I tried to reproduce these results, but failed to get decent
(>100MB/s) performance out of 9p.  I don't have fscache set up, does
that play a part in getting high performance cached writes?

What you describe makes sense, and I have a new patch (attached), but
didn't see drastic improvement in performance of virtio-fs in my
tests.

Thanks,
Miklos
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