From: Jens Axboe <[email protected]>
To: [email protected], [email protected]
Cc: [email protected], [email protected], [email protected],
[email protected], Pavel Begunkov <[email protected]>,
[email protected], Jens Axboe <[email protected]>
Subject: [PATCH] io_uring: Use io_schedule* in cqring wait
Date: Tue, 18 Jul 2023 13:49:15 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
From: Andres Freund <[email protected]>
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: [email protected] # 5.10+
Cc: Pavel Begunkov <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Andres Freund <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[axboe: minor style fixup]
Signed-off-by: Jens Axboe <[email protected]>
---
io_uring/io_uring.c | 15 +++++++++++++--
1 file 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;
}
/*
--
2.40.1
next prev parent reply other threads:[~2023-07-18 19:49 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 19:49 [PATCHSET v2 0/5] Improve async iomap DIO performance Jens Axboe
2023-07-18 19:49 ` Jens Axboe [this message]
2023-07-18 19:50 ` [PATCH] io_uring: Use io_schedule* in cqring wait Jens Axboe
2023-07-18 19:49 ` [PATCH 1/5] iomap: simplify logic for when a dio can get completed inline Jens Axboe
2023-07-18 22:56 ` Dave Chinner
2023-07-19 15:23 ` Jens Axboe
2023-07-18 19:49 ` [PATCH 2/5] fs: add IOCB flags related to passing back dio completions Jens Axboe
2023-07-18 19:49 ` [PATCH 3/5] io_uring/rw: add write support for IOCB_DIO_DEFER Jens Axboe
2023-07-18 19:49 ` [PATCH 4/5] iomap: add local 'iocb' variable in iomap_dio_bio_end_io() Jens Axboe
2023-07-18 19:49 ` [PATCH 5/5] iomap: support IOCB_DIO_DEFER Jens Axboe
2023-07-18 23:50 ` Dave Chinner
2023-07-19 19:55 ` Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2023-07-24 15:35 [PATCH] io_uring: Use io_schedule* in cqring wait Phil Elwell
2023-07-24 15:48 ` Greg KH
2023-07-24 15:50 ` Jens Axboe
2023-07-24 15:58 ` Jens Axboe
2023-07-24 16:07 ` Phil Elwell
2023-07-24 16:08 ` Jens Axboe
2023-07-24 16:48 ` Phil Elwell
2023-07-24 18:22 ` Jens Axboe
2023-07-24 19:22 ` Pavel Begunkov
2023-07-24 20:27 ` Jeff Moyer
2023-07-24 15:48 ` Jens Axboe
2023-07-24 16:16 ` Andres Freund
2023-07-24 16:20 ` Jens Axboe
2023-07-24 17:24 ` Andres Freund
2023-07-24 17:44 ` Jens Axboe
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