linux-kernel - [PATCH 5/5] io_uring: batch put_task

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Date:   Tue, 14 Jul 2020 02:41:56 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] io_uring: batch put_task_struct()

Each put_task_struct() is an atomic_dec. Do that in batches.

Tested io_uring-bench(iopoll,QD=128) with a custom nullblk, where
added ->iopoll() is not optimised at all:

before: 529504 IOPS
after: 	538415 IOPS
diff:	~1.8%

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io_uring.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6f767781351f..3216cc00061b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1761,8 +1761,18 @@ static void io_free_req(struct io_kiocb *req)
 struct req_batch {
 	void *reqs[IO_IOPOLL_BATCH];
 	int to_free;
+
+	struct task_struct	*task;
+	int			task_refs;
 };
 
+static void io_init_req_batch(struct req_batch *rb)
+{
+	rb->to_free = 0;
+	rb->task_refs = 0;
+	rb->task = NULL;
+}
+
 static void __io_req_free_batch_flush(struct io_ring_ctx *ctx,
 				      struct req_batch *rb)
 {
@@ -1776,6 +1786,10 @@ static void io_req_free_batch_finish(struct io_ring_ctx *ctx,
 {
 	if (rb->to_free)
 		__io_req_free_batch_flush(ctx, rb);
+	if (rb->task) {
+		put_task_struct_many(rb->task, rb->task_refs);
+		rb->task = NULL;
+	}
 }
 
 static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req)
@@ -1787,6 +1801,16 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req)
 	if (req->flags & REQ_F_LINK_HEAD)
 		io_queue_next(req);
 
+	if (req->flags & REQ_F_TASK_PINNED) {
+		if (req->task != rb->task && rb->task) {
+			put_task_struct_many(rb->task, rb->task_refs);
+			rb->task = req->task;
+			rb->task_refs = 0;
+		}
+		rb->task_refs++;
+		req->flags &= ~REQ_F_TASK_PINNED;
+	}
+
 	io_dismantle_req(req);
 	rb->reqs[rb->to_free++] = req;
 	if (unlikely(rb->to_free == ARRAY_SIZE(rb->reqs)))
@@ -1809,7 +1833,7 @@ static void io_submit_flush_completions(struct io_comp_state *cs)
 	spin_unlock_irq(&ctx->completion_lock);
 	io_cqring_ev_posted(ctx);
 
-	rb.to_free = 0;
+	io_init_req_batch(&rb);
 	for (i = 0; i < nr; ++i) {
 		req = cs->reqs[i];
 		if (refcount_dec_and_test(&req->refs))
@@ -1973,7 +1997,7 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 	/* order with ->result store in io_complete_rw_iopoll() */
 	smp_rmb();
 
-	rb.to_free = 0;
+	io_init_req_batch(&rb);
 	while (!list_empty(done)) {
 		int cflags = 0;
 
-- 
2.24.0