Hello,
I would like to describe a real-world use case where btrfs does not
perform well for me. I'm recording 60 fps, larger-than-1080p video using
OBS Studio [1] where it is important that the video stream is encoded
and written out to disk in real-time for a prolonged period of time (2-5
hours). The result is a H264 video encoded on the GPU with a data rate
ranging from approximately 10-50 MB/s.
The hardware used is powerful enough to handle this task. When I use a
XFS volume for recording, no matter whether it's a SSD or HDD, the
recording is smooth and no frame drops are reported (OBS has a nice
Stats window where it shows the number of frames dropped due to encoding
lag which seemingly also includes writing the data out to disk).
However, when using a btrfs volume I quickly observe severe, periodic
frame drops. It's not single frames but larger chunks of frames that a
dropped at a time. I tried mounting the volume with nobarrier but to no
avail.
Of course, the simple fix is to use a FS that works for me(TM). However
I thought since this is a common real-world use case I'd describe the
symptoms here in case anyone is interested in analyzing this behavior.
It's not immediately obvious that the FS makes such a difference. Also,
if anyone has an idea what I could try to mitigate this issue (mount or
mkfs options?) I can try that.
I saw this behavior on two different machines with kernels 4.14.13 and
4.14.5, both Arch Linux. btrfs-progs 4.14, OBS 20.1.3-241-gf5c3af1b
built from git.
Best regards
Sebastian
[1] https://github.com/jp9000/obs-studio
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
