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From: Jens Axboe <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>
Subject: [PATCH 5/6] io_uring: use TWA_SIGNAL_NO_IPI if IORING_SETUP_COOP_TASKRUN is used
Date: Mon, 25 Apr 2022 08:21:17 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

If this is set, io_uring will never use an IPI to deliver a task_work
notification. This can be used in the common case where a single task or
thread communicates with the ring, and doesn't rely on
io_uring_cqe_peek().

This provides a noticeable win in performance, both from eliminating
the IPI itself, but also from avoiding interrupting the submitting
task unnecessarily.

Signed-off-by: Jens Axboe <[email protected]>
---
 fs/io_uring.c                 | 8 +++++---
 include/uapi/linux/io_uring.h | 8 ++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7e9ac5fd3a8c..81f5b491c1a5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -11696,9 +11696,10 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 		ctx->user = get_uid(current_user());
 
 	/*
-	 * For SQPOLL, we just need a wakeup, always.
+	 * For SQPOLL, we just need a wakeup, always. For !SQPOLL, if
+	 * COOP_TASKRUN is set, then IPIs are never needed by the app.
 	 */
-	if (ctx->flags & IORING_SETUP_SQPOLL)
+	if (ctx->flags & (IORING_SETUP_SQPOLL|IORING_SETUP_COOP_TASKRUN))
 		ctx->notify_method = TWA_SIGNAL_NO_IPI;
 	else
 		ctx->notify_method = TWA_SIGNAL;
@@ -11800,7 +11801,8 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
 	if (p.flags & ~(IORING_SETUP_IOPOLL | IORING_SETUP_SQPOLL |
 			IORING_SETUP_SQ_AFF | IORING_SETUP_CQSIZE |
 			IORING_SETUP_CLAMP | IORING_SETUP_ATTACH_WQ |
-			IORING_SETUP_R_DISABLED | IORING_SETUP_SUBMIT_ALL))
+			IORING_SETUP_R_DISABLED | IORING_SETUP_SUBMIT_ALL |
+			IORING_SETUP_COOP_TASKRUN))
 		return -EINVAL;
 
 	return  io_uring_create(entries, &p, params);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 5fb52bf32435..4654842ace88 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -104,6 +104,14 @@ enum {
 #define IORING_SETUP_ATTACH_WQ	(1U << 5)	/* attach to existing wq */
 #define IORING_SETUP_R_DISABLED	(1U << 6)	/* start with ring disabled */
 #define IORING_SETUP_SUBMIT_ALL	(1U << 7)	/* continue submit on error */
+/*
+ * Cooperative task running. When requests complete, they often require
+ * forcing the submitter to transition to the kernel to complete. If this
+ * flag is set, work will be done when the task transitions anyway, rather
+ * than force an inter-processor interrupt reschedule. This avoids interrupting
+ * a task running in userspace, and saves an IPI.
+ */
+#define IORING_SETUP_COOP_TASKRUN	(1U << 8)
 
 enum {
 	IORING_OP_NOP,
-- 
2.35.1


  parent reply	other threads:[~2022-04-25 14:21 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-25 14:21 [PATCHSET v3 next 0/5] Add support for non-IPI task_work Jens Axboe
2022-04-25 14:21 ` [PATCH 1/6] task_work: allow TWA_SIGNAL without a rescheduling IPI Jens Axboe
2022-04-25 14:21 ` [PATCH 2/6] io_uring: serialize ctx->rings->sq_flags with atomic_or/and Jens Axboe
2022-04-25 14:21 ` [PATCH 3/6] io-wq: use __set_notify_signal() to wake workers Jens Axboe
2022-04-25 14:21 ` [PATCH 4/6] io_uring: set task_work notify method at init time Jens Axboe
2022-04-25 14:21 ` Jens Axboe [this message]
2022-04-25 14:21 ` [PATCH 6/6] io_uring: add IORING_SETUP_TASKRUN_FLAG Jens Axboe
  -- strict thread matches above, loose matches on Subject: below --
2022-04-26  1:48 [PATCHSET v4 next 0/5] Add support for non-IPI task_work Jens Axboe
2022-04-26  1:49 ` [PATCH 5/6] io_uring: use TWA_SIGNAL_NO_IPI if IORING_SETUP_COOP_TASKRUN is used Jens Axboe

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