FAILED: patch "[PATCH] io_uring: Use io_schedule* in cqring wait" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 8a796565cec3601071cbbd27d6304e202019d014
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023071620-litigate-debunk-939a@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

8a796565cec3 ("io_uring: Use io_schedule* in cqring wait") d33a39e57768 ("io_uring: keep timeout in io_wait_queue")
46ae7eef44f6 ("io_uring: optimise non-timeout waiting")
846072f16eed ("io_uring: mimimise io_cqring_wait_schedule") 3fcf19d592d5 ("io_uring: parse check_cq out of wq waiting") 12521a5d5cb7 ("io_uring: fix CQ waiting timeout handling") 52ea806ad983 ("io_uring: finish waiting before flushing overflow entries") 35d90f95cfa7 ("io_uring: include task_work run after scheduling in wait for events") 1b346e4aa8e7 ("io_uring: don't check overflow flush failures") a85381d8326d ("io_uring: skip overflow CQE posting for dying ring")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8a796565cec3601071cbbd27d6304e202019d014 Mon Sep 17 00:00:00 2001
From: Andres Freund <[email protected]>
Date: Fri, 7 Jul 2023 09:20:07 -0700
Subject: [PATCH] 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.

index e8096d502a7c..7505de2428e0 100644
@@ -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;
 }
 
 /*

Here's one for 6.1-stable.

Jens Axboe

From 71fc76b239a1c980c11821916d1d6785bc177c5c Mon Sep 17 00:00:00 2001
From: Andres Freund <[email protected]>
Date: Sun, 16 Jul 2023 12:13:06 -0600
Subject: [PATCH] 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.

---
 io_uring/io_uring.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

index cc35aba1e495..de117d3424b2 100644
@@ -2346,7 +2346,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 					  struct io_wait_queue *iowq,
 					  ktime_t *timeout)
 {
-	int ret;
+	int token, ret;
 	unsigned long check_cq;
 
 	/* make sure we run task_work before checking for signals */

@@ -2362,9 +2362,18 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 		if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT))
 			return -EBADR;
 	}
+
+	/*
+	 * 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 (!schedule_hrtimeout(timeout, HRTIMER_MODE_ABS))
-		return -ETIME;
-	return 1;
+		ret = -ETIME;
+	io_schedule_finish(token);
+	return ret;
 }
 
 /*

2.40.1

Hi,

Thanks for working on that!

Ah shoot yes indeed. Greg, can you drop the 5.10/5.15/6.1 ones for now? I'll get it sorted tomorrow. Sorry about that, and thanks for catching that Andres!

Jens Axboe

Sure, will go drop it now, thanks.

greg k-h

Greg, can you pick up these two for 5.10-stable and 5.15-stable? While running testing, noticed another backport that was missing, so added that as we..

Jens Axboe

From 4e214e7e01158a87308a17766706159bca472855 Mon Sep 17 00:00:00 2001
From: Jens Axboe <[email protected]>
Date: Mon, 17 Jul 2023 10:27:20 -0600
Subject: [PATCH 2/2] io_uring: add reschedule point to handle_tw_list()

Commit f58680085478dd292435727210122960d38e8014 upstream.

If CONFIG_PREEMPT_NONE is set and the task_work chains are long, we could be running into issues blocking others for too long. Add a reschedule check in handle_tw_list(), and flush the ctx if we need to reschedule.

---
 io_uring/io_uring.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

index 33d4a2871dbb..eae7a3d89397 100644
@@ -2216,9 +2216,12 @@ static void tctx_task_work(struct callback_head *cb)
 			}
 			req->io_task_work.func(req, &locked);
 			node = next;
+			if (unlikely(need_resched())) {
+				ctx_flush_and_put(ctx, &locked);
+				ctx = NULL;
+				cond_resched();
+			}
 		} while (node);
-
-		cond_resched();
 	}
 
 	ctx_flush_and_put(ctx, &locked);

2.40.1

From c8c88d523c89e0ac8affbf2fd57def82e0d5d4bf Mon Sep 17 00:00:00 2001
From: Andres Freund <[email protected]>
Date: Sun, 16 Jul 2023 12:07:03 -0600
Subject: [PATCH 1/2] io_uring: Use io_schedule* in cqring wait

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.

---
 io_uring/io_uring.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

index e633799c9cea..33d4a2871dbb 100644
@@ -7785,7 +7785,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 					  struct io_wait_queue *iowq,
 					  ktime_t *timeout)
 {
-	int ret;
+	int token, ret;
 
 	/* make sure we run task_work before checking for signals */
 	ret = io_run_task_work_sig();

@@ -7795,9 +7795,17 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 	if (test_bit(0, &ctx->check_cq_overflow))
 		return 1;
 
+	/*
+	 * 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 = 1;
 	if (!schedule_hrtimeout(timeout, HRTIMER_MODE_ABS))
-		return -ETIME;
-	return 1;
+		ret = -ETIME;
+	io_schedule_finish(token);
+	return ret;
 }
 
 /*

2.40.1

And here's a corrected one for 6.1.

Jens Axboe

From f5f24ec27340daf12177fd09c2d107a589cbf527 Mon Sep 17 00:00:00 2001
From: Andres Freund <[email protected]>
Date: Sun, 16 Jul 2023 12:13:06 -0600
Subject: [PATCH] io_uring: Use io_schedule* in cqring wait

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.

---
 io_uring/io_uring.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

index cc35aba1e495..6d7b358e71f1 100644
@@ -2346,7 +2346,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 					  struct io_wait_queue *iowq,
 					  ktime_t *timeout)
 {
-	int ret;
+	int token, ret;
 	unsigned long check_cq;
 
 	/* make sure we run task_work before checking for signals */

@@ -2362,9 +2362,18 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 		if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT))
 			return -EBADR;
 	}
+
+	/*
+	 * 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 = 1;
 	if (!schedule_hrtimeout(timeout, HRTIMER_MODE_ABS))
-		return -ETIME;
-	return 1;
+		ret = -ETIME;
+	io_schedule_finish(token);
+	return ret;
 }
 
 /*

2.40.1

Hi,

Thanks! LGTM.

Greetings,

Andres Freund

All now queued up, thanks.

greg k-h

Great, thanks Greg!

Jens Axboe