io_uring: add support for hybrid IOPOLL

A new hybrid poll is implemented on the io_uring layer. Once an IO is
issued, it will not poll immediately, but rather block first and re-run
before IO complete, then poll to reap IO. While this poll method could
be a suboptimal solution when running on a single thread, it offers
performance lower than regular polling but higher than IRQ, and CPU
utilization is also lower than polling.

To use hybrid polling, the ring must be setup with both the
IORING_SETUP_IOPOLL and IORING_SETUP_HYBRID)IOPOLL flags set. Hybrid
polling has the same restrictions as IOPOLL, in that commands must
explicitly support it.

Signed-off-by: hexue <xue01.he@samsung.com>
Link: https://lore.kernel.org/r/20241101091957.564220-2-xue01.he@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 88 insertions, 12 deletions

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 44a772013c09..f08ea7fd5998 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -307,6 +307,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 		goto err;
 
 	ctx->flags = p->flags;
+	ctx->hybrid_poll_time = LLONG_MAX;
 	atomic_set(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT);
 	init_waitqueue_head(&ctx->sqo_sq_wait);
 	INIT_LIST_HEAD(&ctx->sqd_list);
@@ -3630,6 +3631,11 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY))
 		static_branch_inc(&io_key_has_sqarray);
 
+	/* HYBRID_IOPOLL only valid with IOPOLL */
+	if ((ctx->flags & (IORING_SETUP_IOPOLL|IORING_SETUP_HYBRID_IOPOLL)) ==
+			IORING_SETUP_HYBRID_IOPOLL)
+		return -EINVAL;
+
 	if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
 	    !(ctx->flags & IORING_SETUP_IOPOLL) &&
 	    !(ctx->flags & IORING_SETUP_SQPOLL))
@@ -3785,7 +3791,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
 			IORING_SETUP_SQE128 | IORING_SETUP_CQE32 |
 			IORING_SETUP_SINGLE_ISSUER | IORING_SETUP_DEFER_TASKRUN |
 			IORING_SETUP_NO_MMAP | IORING_SETUP_REGISTERED_FD_ONLY |
-			IORING_SETUP_NO_SQARRAY))
+			IORING_SETUP_NO_SQARRAY | IORING_SETUP_HYBRID_IOPOLL))
 		return -EINVAL;
 
 	return io_uring_create(entries, &p, params);
diff --git a/io_uring/rw.c b/io_uring/rw.c
index 30448f343c7f..1ea6be2ccc90 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -817,6 +817,11 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode, int rw_type)
 		kiocb->ki_flags |= IOCB_HIPRI;
 		kiocb->ki_complete = io_complete_rw_iopoll;
 		req->iopoll_completed = 0;
+		if (ctx->flags & IORING_SETUP_HYBRID_IOPOLL) {
+			/* make sure every req only blocks once*/
+			req->flags &= ~REQ_F_IOPOLL_STATE;
+			req->iopoll_start = ktime_get_ns();
+		}
 	} else {
 		if (kiocb->ki_flags & IOCB_HIPRI)
 			return -EINVAL;
@@ -1115,6 +1120,78 @@ void io_rw_fail(struct io_kiocb *req)
 	io_req_set_res(req, res, req->cqe.flags);
 }
 
+static int io_uring_classic_poll(struct io_kiocb *req, struct io_comp_batch *iob,
+				unsigned int poll_flags)
+{
+	struct file *file = req->file;
+
+	if (req->opcode == IORING_OP_URING_CMD) {
+		struct io_uring_cmd *ioucmd;
+
+		ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
+		return file->f_op->uring_cmd_iopoll(ioucmd, iob, poll_flags);
+	} else {
+		struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
+
+		return file->f_op->iopoll(&rw->kiocb, iob, poll_flags);
+	}
+}
+
+static u64 io_hybrid_iopoll_delay(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+	struct hrtimer_sleeper timer;
+	enum hrtimer_mode mode;
+	ktime_t kt;
+	u64 sleep_time;
+
+	if (req->flags & REQ_F_IOPOLL_STATE)
+		return 0;
+
+	if (ctx->hybrid_poll_time == LLONG_MAX)
+		return 0;
+
+	/* Using half the running time to do schedule */
+	sleep_time = ctx->hybrid_poll_time / 2;
+
+	kt = ktime_set(0, sleep_time);
+	req->flags |= REQ_F_IOPOLL_STATE;
+
+	mode = HRTIMER_MODE_REL;
+	hrtimer_init_sleeper_on_stack(&timer, CLOCK_MONOTONIC, mode);
+	hrtimer_set_expires(&timer.timer, kt);
+	set_current_state(TASK_INTERRUPTIBLE);
+	hrtimer_sleeper_start_expires(&timer, mode);
+
+	if (timer.task)
+		io_schedule();
+
+	hrtimer_cancel(&timer.timer);
+	__set_current_state(TASK_RUNNING);
+	destroy_hrtimer_on_stack(&timer.timer);
+	return sleep_time;
+}
+
+static int io_uring_hybrid_poll(struct io_kiocb *req,
+				struct io_comp_batch *iob, unsigned int poll_flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	u64 runtime, sleep_time;
+	int ret;
+
+	sleep_time = io_hybrid_iopoll_delay(ctx, req);
+	ret = io_uring_classic_poll(req, iob, poll_flags);
+	runtime = ktime_get_ns() - req->iopoll_start - sleep_time;
+
+	/*
+	 * Use minimum sleep time if we're polling devices with different
+	 * latencies. We could get more completions from the faster ones.
+	 */
+	if (ctx->hybrid_poll_time > runtime)
+		ctx->hybrid_poll_time = runtime;
+
+	return ret;
+}
+
 int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 {
 	struct io_wq_work_node *pos, *start, *prev;
@@ -1131,7 +1208,6 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 
 	wq_list_for_each(pos, start, &ctx->iopoll_list) {
 		struct io_kiocb *req = container_of(pos, struct io_kiocb, comp_list);
-		struct file *file = req->file;
 		int ret;
 
 		/*
@@ -1142,17 +1218,11 @@ int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
 		if (READ_ONCE(req->iopoll_completed))
 			break;
 
-		if (req->opcode == IORING_OP_URING_CMD) {
-			struct io_uring_cmd *ioucmd;
-
-			ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-			ret = file->f_op->uring_cmd_iopoll(ioucmd, &iob,
-								poll_flags);
-		} else {
-			struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
+		if (ctx->flags & IORING_SETUP_HYBRID_IOPOLL)
+			ret = io_uring_hybrid_poll(req, &iob, poll_flags);
+		else
+			ret = io_uring_classic_poll(req, &iob, poll_flags);
 
-			ret = file->f_op->iopoll(&rw->kiocb, &iob, poll_flags);
-		}
 		if (unlikely(ret < 0))
 			return ret;
 		else if (ret)