Re: problem with fio --client and latency logs

[Jens Axboe <axboe@kernel.dk>]

On 05/26/2016 01:11 PM, Ben England wrote:
> recently I noticed a problem in master branch when fio --client is used.  latency logs generated with it have large numbers of "0, 0, 0, 0" records at the end of the file.  I have a simple reproducer fio jobfile:
>
> --------- reproducer.fiojob ----
> [global]
> numjobs=1
> directory=/var/tmp
>
> [shared-files]
> rw=randread
> write_lat_log=1thr
> ioengine=sync
> bs=4k      # I/O size
> filesize=1g  # file size
> runtime=20
> -------------
>
> If you run this job file like this:
>
> # fio --server --daemonize=/var/run/fiosvr.pid
> # fio --client=localhost reproducer.fiojob
>
> You get the latency log 1thr_clat.1.log with the 0 records at the end.  If you run the same job file with:
>
> # fio reproducer.fiojob
>
> You don't get the 0 records.  This explains why Ceph CBT does not have the problem, for example.
>
> I bisected fio history using git until I found the first commit that failed:
>
> -------
> commit 0cba0f919ee6af7dd65df436884336cff9c903f9
> Author: Jens Axboe <axboe@fb.com>
> Date:   Thu Dec 17 14:54:15 2015 -0700
>
>      client/server: transparent handling of storing compressed logs
>
>      Signed-off-by: Jens Axboe <axboe@fb.com>
> ------
>
> I could use some help figuring out what went wrong at this point, the diffs were complicated but it seemed possible that this commit was related to my problem.

I have a good idea what this might be, I'll take a look at it.

-- 
Jens Axboe