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. Thanks. [1] https://bbs.archlinux.org/viewtopic.php?id=287343 [2] https://bugzilla.kernel.org/show_bug.cgi?id=217700 [3] https://bugzilla.kernel.org/show_bug.cgi?id=217699 -- Oleksandr Natalenko (post-factum)
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