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From: Jens Axboe <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>
Subject: [PATCH 3/4] io-wq: briefly spin for new work after finishing work
Date: Mon,  9 Dec 2019 16:18:53 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

To avoid going to sleep only to get woken shortly thereafter, spin
briefly for new work upon completion of work.

Signed-off-by: Jens Axboe <[email protected]>
---
 fs/io-wq.c | 24 ++++++++++++++++++++++--
 fs/io-wq.h |  7 ++++---
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 6b663ddceb42..90c4978781fb 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -491,26 +491,46 @@ static void io_worker_handle_work(struct io_worker *worker)
 	} while (1);
 }
 
+static inline void io_worker_spin_for_work(struct io_wqe *wqe)
+{
+	int i = 0;
+
+	while (++i < 1000) {
+		if (io_wqe_run_queue(wqe))
+			break;
+		if (need_resched())
+			break;
+		cpu_relax();
+	}
+}
+
 static int io_wqe_worker(void *data)
 {
 	struct io_worker *worker = data;
 	struct io_wqe *wqe = worker->wqe;
 	struct io_wq *wq = wqe->wq;
+	bool did_work;
 
 	io_worker_start(wqe, worker);
 
+	did_work = false;
 	while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
 		set_current_state(TASK_INTERRUPTIBLE);
+loop:
+		if (did_work)
+			io_worker_spin_for_work(wqe);
 		spin_lock_irq(&wqe->lock);
 		if (io_wqe_run_queue(wqe)) {
 			__set_current_state(TASK_RUNNING);
 			io_worker_handle_work(worker);
-			continue;
+			did_work = true;
+			goto loop;
 		}
+		did_work = false;
 		/* drops the lock on success, retry */
 		if (__io_worker_idle(wqe, worker)) {
 			__release(&wqe->lock);
-			continue;
+			goto loop;
 		}
 		spin_unlock_irq(&wqe->lock);
 		if (signal_pending(current))
diff --git a/fs/io-wq.h b/fs/io-wq.h
index 7c333a28e2a7..fb993b2bd0ef 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -35,7 +35,8 @@ static inline void wq_list_add_tail(struct io_wq_work_node *node,
 				    struct io_wq_work_list *list)
 {
 	if (!list->first) {
-		list->first = list->last = node;
+		list->last = node;
+		WRITE_ONCE(list->first, node);
 	} else {
 		list->last->next = node;
 		list->last = node;
@@ -47,7 +48,7 @@ static inline void wq_node_del(struct io_wq_work_list *list,
 			       struct io_wq_work_node *prev)
 {
 	if (node == list->first)
-		list->first = node->next;
+		WRITE_ONCE(list->first, node->next);
 	if (node == list->last)
 		list->last = prev;
 	if (prev)
@@ -58,7 +59,7 @@ static inline void wq_node_del(struct io_wq_work_list *list,
 #define wq_list_for_each(pos, prv, head)			\
 	for (pos = (head)->first, prv = NULL; pos; prv = pos, pos = (pos)->next)
 
-#define wq_list_empty(list)	((list)->first == NULL)
+#define wq_list_empty(list)	(READ_ONCE((list)->first) == NULL)
 #define INIT_WQ_LIST(list)	do {				\
 	(list)->first = NULL;					\
 	(list)->last = NULL;					\
-- 
2.24.0


  parent reply	other threads:[~2019-12-09 23:19 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-09 23:18 [PATCHSET 0/4] io_uring patches for 5.5-rc Jens Axboe
2019-12-09 23:18 ` [PATCH 1/4] io_uring: allow unbreakable links Jens Axboe
2019-12-10 10:13   ` Pavel Begunkov
2019-12-10 15:13     ` Jens Axboe
2019-12-09 23:18 ` [PATCH 2/4] io-wq: remove worker->wait waitqueue Jens Axboe
2019-12-09 23:18 ` Jens Axboe [this message]
2019-12-09 23:18 ` [PATCH 4/4] io_uring: sqthread should grab ctx->uring_lock for submissions Jens Axboe

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