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@xxxxxxxxxxx> > > > > > > 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@xxxxxxxxxxxxxxx # 5.10+ > > > Cc: Pavel Begunkov <asml.silence@xxxxxxxxx> > > > Cc: io-uring@xxxxxxxxxxxxxxx > > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > > Signed-off-by: Andres Freund <andres@xxxxxxxxxxx> > > > Link: https://lore.kernel.org/r/20230707162007.194068-1-andres@xxxxxxxxxxx > > > [axboe: minor style fixup] > > > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > --- > > > 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 > -- Oleksandr Natalenko (post-factum)
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