diff options
| author | Andres Freund <andres@anarazel.de> | 2023-07-07 09:20:07 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2023-07-07 11:24:29 -0600 |
| commit | 8a796565cec3601071cbbd27d6304e202019d014 (patch) | |
| tree | b8f670a0711a9a2eb726a7d55239677f7db66112 /io_uring | |
| parent | dfbe5561ae9339516a3742a3fbd678609ad59fd0 (diff) | |
io_uring: Use io_schedule* in cqring wait
I observed poor performance of io_uring compared to synchronous IO. That
turns out to be caused by deeper CPU idle states entered with io_uring,
due to io_uring using plain schedule(), whereas synchronous IO uses
io_schedule().
The losses due to this are substantial. On my cascade lake workstation,
t/io_uring from the fio repository e.g. yields regressions between 20%
and 40% with the following command:
./t/io_uring -r 5 -X0 -d 1 -s 1 -c 1 -p 0 -S$use_sync -R 0 /mnt/t2/fio/write.0.0
This is repeatable with different filesystems, using raw block devices
and using different block devices.
Use io_schedule_prepare() / io_schedule_finish() in
io_cqring_wait_schedule() to address the difference.
After that using io_uring is on par or surpassing synchronous IO (using
registered files etc makes it reliably win, but arguably is a less fair
comparison).
There are other calls to schedule() in io_uring/, but none immediately
jump out to be similarly situated, so I did not touch them. Similarly,
it's possible that mutex_lock_io() should be used, but it's not clear if
there are cases where that matters.
Cc: stable@vger.kernel.org # 5.10+
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: io-uring@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andres Freund <andres@anarazel.de>
Link: https://lore.kernel.org/r/20230707162007.194068-1-andres@anarazel.de
[axboe: minor style fixup]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'io_uring')
| -rw-r--r-- | io_uring/io_uring.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index e8096d502a7c..7505de2428e0 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2489,6 +2489,8 @@ int io_run_task_work_sig(struct io_ring_ctx *ctx) static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, struct io_wait_queue *iowq) { + int token, ret; + if (unlikely(READ_ONCE(ctx->check_cq))) return 1; if (unlikely(!llist_empty(&ctx->work_llist))) @@ -2499,11 +2501,20 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, return -EINTR; if (unlikely(io_should_wake(iowq))) return 0; + + /* + * Use io_schedule_prepare/finish, so cpufreq can take into account + * that the task is waiting for IO - turns out to be important for low + * QD IO. + */ + token = io_schedule_prepare(); + ret = 0; if (iowq->timeout == KTIME_MAX) schedule(); else if (!schedule_hrtimeout(&iowq->timeout, HRTIMER_MODE_ABS)) - return -ETIME; - return 0; + ret = -ETIME; + io_schedule_finish(token); + return ret; } /* |