On neděle 23. července 2023 12:50:30 CEST Greg Kroah-Hartman wrote:
On Sun, Jul 23, 2023 at 11:39:42AM +0200, Oleksandr Natalenko wrote:
Hello.
On neděle 16. července 2023 21:50:53 CEST Greg Kroah-Hartman wrote:
From: Andres Freund andres@anarazel.de
commit 8a796565cec3601071cbbd27d6304e202019d014 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
io_uring/io_uring.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2575,6 +2575,8 @@ int io_run_task_work_sig(struct io_ring_ 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)))
@@ -2585,11 +2587,20 @@ static inline int io_cqring_wait_schedul 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;
} /*
Reportedly, this caused a regression as reported in [1] [2] [3]. Not only v6.4.4 is affected, v6.1.39 is affected too.
Reverting this commit fixes the issue.
Please check.
Is this also an issue in 6.5-rc2?
As per [1], yes.
[1] https://bugzilla.kernel.org/show_bug.cgi?id=217699#c4
thanks,
greg k-h