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On Thu, Dec 27, 2018 at 10:57:21AM +0800, jiangyiwen wrote:

[..]
> >>
> >> 4. When I use fio with psync, write/read only 20% improve than 9p, I think
> >> psync can be more used than mmap. This user-case may need to improved.
> > 
> > Can you send me your fio job. I want to try it out.
> > 
> 
> fio -filename=/mnt/virtio_fs/file -rw=read -bs=4k -size=6G -iodepth=1 -ioengine=psync -numjobs=1 -group_reporting -name=xxx -time_based -runtime=120

Ok, finally I tried this in bunch of configurations. without dax and
cache=none, I see roughly 100% improvement.

cache=none
==========
virtio-9p: 28MB/s
virtio-fs: 59MB/s

Above is without dax enabled and libfuse daemon filters O_DIRECT flag on
host so that file will be cached in host (despite the fact guest opened
it with O_DIRECT). 

I then tried "cache=always" and did direct I/O from guest. This will avoid
page cache in guest but will use page cache on host.

cache=always
===========
virtio-fs: 52MB/s
virtio-fs (dax): 175MB/s

Notice that with dax performance is alsmost 5x times better as compared to
virtio-9p.

Following is my fio job for testing.

=======================================
[global]
name=fio-psync
rw=read
direct=1
numjobs=1
runtime=60
bs=4k

[file1]
size=6G
ioengine=psync
iodepth=1
filename=fio-psync-file
========================================

So I think even without dax, performance improvement is significant and
enabling dax speeds it up very significantly.

Thanks
Vivek