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

[Miklos Szeredi]

On Thu, Aug 22, 2019 at 2:48 PM wangyan <wangyan122 at huawei.com> wrote:
>
> On 2019/8/22 19:43, Miklos Szeredi wrote:
> > On Thu, Aug 22, 2019 at 2:59 AM wangyan <wangyan122 at huawei.com> wrote:
> >> I will test it when I get the patch, and post the compared result with
> >> 9p.
> >
> > Could you please try the attached patch?  My guess is that it should
> > improve the performance, perhaps by a big margin.
> >
> > Further improvement is possible by eliminating page copies, but that
> > is less trivial.
> >
> > Thanks,
> > Miklos
> >
> Using the same test model. And the test result is:
>         1. Latency
>                 virtiofs: avg-lat is 15.40 usec, bigger than before(6.64 usec).
>                 4K: (g=0): rw=write, bs=4K-4K/4K-4K/4K-4K, ioengine=psync, iodepth=1
>                 fio-2.13
>                 Starting 1 process
>                 Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/142.4MB/0KB /s] [0/36.5K/0
> iops] [eta 00m:00s]
>                 4K: (groupid=0, jobs=1): err= 0: pid=5528: Thu Aug 22 20:39:07 2019
>                   write: io=6633.2MB, bw=226404KB/s, iops=56600, runt= 30001msec
>                         clat (usec): min=2, max=40403, avg=14.77, stdev=33.71
>                          lat (usec): min=3, max=40404, avg=15.40, stdev=33.74
>
>         2. Bandwidth
>                 virtiofs: bandwidth is 280840KB/s, lower than before(691894KB/s).
>                 1M: (g=0): rw=write, bs=1M-1M/1M-1M/1M-1M, ioengine=psync, iodepth=1
>                 fio-2.13
>                 Starting 1 process
>                 Jobs: 1 (f=1): [f(1)] [100.0% done] [0KB/29755KB/0KB /s] [0/29/0 iops]
> [eta 00m:00s]
>                 1M: (groupid=0, jobs=1): err= 0: pid=5550: Thu Aug 22 20:41:28 2019
>                   write: io=8228.0MB, bw=280840KB/s, iops=274, runt= 30001msec
>                         clat (usec): min=362, max=11038, avg=3571.33, stdev=1062.72
>                          lat (usec): min=411, max=11093, avg=3628.39, stdev=1064.53
>
> According to the result, the patch doesn't work and make it worse than
> before.

Is server started with "-owriteback"?

Thanks,
Miklos