From: "Theodore Ts'o" <tytso@mit.edu>
To: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Cc: linux-ext4@vger.kernel.org, adilger.kernel@dilger.ca
Subject: Re: [RFC] jbd2: add new "stats" proc file
Date: Mon, 3 Jun 2019 10:38:01 -0400 [thread overview]
Message-ID: <20190603143801.GA3048@mit.edu> (raw)
In-Reply-To: <20190603124238.9050-1-xiaoguang.wang@linux.alibaba.com>
On Mon, Jun 03, 2019 at 08:42:38PM +0800, Xiaoguang Wang wrote:
> /proc/fs/jbd2/${device}/info only shows whole average statistical
> info about jbd2's life cycle, but it can not show jbd2 info in
> specified time interval and sometimes this capability is very useful
> for trouble shooting. For example, we can not see how rs_locked and
> rs_flushing grows in specified time interval, but these two indexes
> can explain some reasons for app's behaviours.
We actually had something like this, but we removed it in commit
bf6993276f7: "jbd2: Use tracepoints for history file". The idea was
that you can get the same information using the jbd2_run_tracepoints
# echo jbd2_run_stats > /sys/kernel/debug/tracing/set_event
# cat /sys/kernel/debug/tracing/trace_pipe
... which will produce output like this:
jbd2/vdg-8-293 [000] ...2 122.822487: jbd2_run_stats: dev 254,96 tid 4403 wait 0 request_delay 0 running 4 locked 0 flushing 0 logging 7 handle_count 98 blocks 3 blocks_logged 4
jbd2/vdg-8-293 [000] ...2 122.833101: jbd2_run_stats: dev 254,96 tid 4404 wait 0 request_delay 0 running 14 locked 0 flushing 0 logging 4 handle_count 198 blocks 1 blocks_logged 2
jbd2/vdg-8-293 [000] ...2 122.839325: jbd2_run_stats: dev 254,96 tid 4405 wait
With eBPF, we should be able to do something even more user friendly.
BTW, if you are looking to try to optimize jbd2, a good thing to do is
to take a look at jbd2_handle_stats, filtered on ones where the
interval is larger than some cut-off. Ideally, the time between a
handle getting started and stopped should be as small as possible,
because if a transaction is trying to close, an open handle will get
in the way of that, and other CPU's will be stuck waiting for handle
to complete. This means that pre-reading blocks before starting a
handle, etc., is a really good idea. And monitoring jbd2_handle_stats
is a good way to find potential spots to topimize in ext4.
- Ted
next prev parent reply other threads:[~2019-06-03 14:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-03 12:42 [RFC] jbd2: add new "stats" proc file Xiaoguang Wang
2019-06-03 14:38 ` Theodore Ts'o [this message]
2019-06-05 7:05 ` Xiaoguang Wang
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