From: Dmitry Shulyak <yashulyak@gmail.com>
To: io-uring@vger.kernel.org
Subject: Very low write throughput on file opened with O_SYNC/O_DSYNC
Date: Mon, 17 Aug 2020 14:46:37 +0300 [thread overview]
Message-ID: <CAF-ewDrOHDxpSAm8Or37m-k5K4u+b3H2YwnA-KpkFuVa+1vBOw@mail.gmail.com> (raw)
Hi everyone,
I noticed in iotop that all writes are executed by the same thread
(io_wqe_worker-0). This is a significant problem if I am using files
with mentioned flags. Not the case with reads, requests are
multiplexed over many threads (note the different name
io_wqe_worker-1). The problem is not specific to O_SYNC, in the
general case I can get higher throughput with thread pool and regular
system calls, but specifically with O_SYNC the throughput is the same
as if I were using a single thread for writing.
The setup is always the same, ring per thread with shared workers pool
(IORING_SETUP_ATTACH_WQ), and high submission rate. Also, it is
possible to get around this performance issue by using separate worker
pools, but then I have to load balance workload between many rings for
perf gains.
I thought that it may have something to do with the IOSQE_ASYNC flag,
but setting it had no effect.
Is it expected behavior? Are there any other solutions, except
creating many rings with isolated worker pools?
next reply other threads:[~2020-08-17 11:46 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-17 11:46 Dmitry Shulyak [this message]
2020-08-17 11:58 ` Very low write throughput on file opened with O_SYNC/O_DSYNC Dmitry Shulyak
2020-08-17 14:29 ` Jens Axboe
2020-08-17 15:49 ` Dmitry Shulyak
2020-08-17 16:17 ` Jens Axboe
2020-08-18 16:09 ` Dmitry Shulyak
2020-08-18 16:42 ` Jens Axboe
2020-08-19 7:55 ` Dmitry Shulyak
2020-08-21 13:43 ` Dmitry Shulyak
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAF-ewDrOHDxpSAm8Or37m-k5K4u+b3H2YwnA-KpkFuVa+1vBOw@mail.gmail.com \
--to=yashulyak@gmail.com \
--cc=io-uring@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).