Re: [PATCH v3 1/4] btrfs: add read_policy latency

Michal Rostecki
2021-01-20T14:53:59Z

On Wed, Jan 20, 2021 at 08:30:56PM +0800, Anand Jain wrote:
> I ran fio tests again, now with dstat in an another window. I don't
> notice any such stalls, the read numbers went continuous until fio
> finished. Could you please check with the below fio command, also
> could you please share your fio command options.

That's the fio config I used:

https://gitlab.com/vadorovsky/playground/-/blob/master/fio/btrfs-raid1-seqread.fio

The main differences seem to be:
- the number of jobs (I used the number of CPU threads)
- direct vs buffered I/O

>
> fio \
> --filename=/btrfs/largefile \
> --directory=/btrfs \
> --filesize=50G \
> --size=50G \
> --bs=64k \
> --ioengine=libaio \
> --rw=read \
> --direct=1 \
> --numjobs=1 \
> --group_reporting \
> --thread \
> --name iops-test-job
>
> It is system specific?

With this command, dstat output looks good:

https://paste.opensuse.org/view/simple/93159623

So I think it might be specific to whether we test direct of buffered
I/O. Or to the number of jobs (single vs multiple jobs). Since the most
of I/O on production environments is usually buffered, I think we should
test with direct=0 too.

Cheers,
Michal