[PATCH 8/9] io-wq: batch the handling of fixed worker private works

[Hao Xu]

From: Hao Xu <howeyxu@xxxxxxxxxxx>

Reduce acct->lock contension by batching the handling of private work
list for fixed_workers.

Signed-off-by: Hao Xu <howeyxu@xxxxxxxxxxx>
---
 fs/io-wq.c | 42 +++++++++++++++++++++++++++++++++---------
 fs/io-wq.h |  5 +++++
 2 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index aaa9cea7d39a..df2d480395e8 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -540,8 +540,23 @@ static bool io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
 	return ret;
 }
 
+static inline void conditional_acct_lock(struct io_wqe_acct *acct,
+					 bool needs_lock)
+{
+	if (needs_lock)
+		raw_spin_lock(&acct->lock);
+}
+
+static inline void conditional_acct_unlock(struct io_wqe_acct *acct,
+					   bool needs_lock)
+{
+	if (needs_lock)
+		raw_spin_unlock(&acct->lock);
+}
+
 static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
-					   struct io_worker *worker)
+					   struct io_worker *worker,
+					   bool needs_lock)
 	__must_hold(acct->lock)
 {
 	struct io_wq_work_node *node, *prev;
@@ -549,6 +564,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
 	unsigned int stall_hash = -1U;
 	struct io_wqe *wqe = worker->wqe;
 
+	conditional_acct_lock(acct, needs_lock);
 	wq_list_for_each(node, prev, &acct->work_list) {
 		unsigned int hash;
 
@@ -557,6 +573,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
 		/* not hashed, can run anytime */
 		if (!io_wq_is_hashed(work)) {
 			wq_list_del(&acct->work_list, node, prev);
+			conditional_acct_unlock(acct, needs_lock);
 			return work;
 		}
 
@@ -568,6 +585,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
 		if (!test_and_set_bit(hash, &wqe->wq->hash->map)) {
 			wqe->hash_tail[hash] = NULL;
 			wq_list_cut(&acct->work_list, &tail->list, prev);
+			conditional_acct_unlock(acct, needs_lock);
 			return work;
 		}
 		if (stall_hash == -1U)
@@ -584,15 +602,16 @@ static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
 		 * work being added and clearing the stalled bit.
 		 */
 		set_bit(IO_ACCT_STALLED_BIT, &acct->flags);
-		raw_spin_unlock(&acct->lock);
+		conditional_acct_unlock(acct, needs_lock);
 		unstalled = io_wait_on_hash(wqe, stall_hash);
-		raw_spin_lock(&acct->lock);
+		conditional_acct_lock(acct, needs_lock);
 		if (unstalled) {
 			clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
 			if (wq_has_sleeper(&wqe->wq->hash->wait))
 				wake_up(&wqe->wq->hash->wait);
 		}
 	}
+	conditional_acct_unlock(acct, needs_lock);
 
 	return NULL;
 }
@@ -626,7 +645,7 @@ static void io_assign_current_work(struct io_worker *worker,
 static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work);
 
 static void io_worker_handle_work(struct io_worker *worker,
-				  struct io_wqe_acct *acct)
+				  struct io_wqe_acct *acct, bool needs_lock)
 {
 	struct io_wqe *wqe = worker->wqe;
 	struct io_wq *wq = wqe->wq;
@@ -642,9 +661,7 @@ static void io_worker_handle_work(struct io_worker *worker,
 		 * can't make progress, any work completion or insertion will
 		 * clear the stalled flag.
 		 */
-		raw_spin_lock(&acct->lock);
-		work = io_get_next_work(acct, worker);
-		raw_spin_unlock(&acct->lock);
+		work = io_get_next_work(acct, worker, needs_lock);
 		if (work) {
 			__io_worker_busy(wqe, worker);
 
@@ -701,12 +718,19 @@ static void io_worker_handle_work(struct io_worker *worker,
 
 static inline void io_worker_handle_private_work(struct io_worker *worker)
 {
-	io_worker_handle_work(worker, &worker->acct);
+	struct io_wqe_acct acct;
+
+	raw_spin_lock(&worker->acct.lock);
+	acct = worker->acct;
+	wq_list_clean(&worker->acct.work_list);
+	worker->acct.nr_works = 0;
+	raw_spin_unlock(&worker->acct.lock);
+	io_worker_handle_work(worker, &acct, false);
 }
 
 static inline void io_worker_handle_public_work(struct io_worker *worker)
 {
-	io_worker_handle_work(worker, io_wqe_get_acct(worker));
+	io_worker_handle_work(worker, io_wqe_get_acct(worker), true);
 }
 
 static int io_wqe_worker(void *data)
diff --git a/fs/io-wq.h b/fs/io-wq.h
index ba6eee76d028..ef3ce577e6b7 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -40,6 +40,11 @@ struct io_wq_work_list {
 	(list)->first = NULL;					\
 } while (0)
 
+static inline void wq_list_clean(struct io_wq_work_list *list)
+{
+	list->first = list->last = NULL;
+}
+
 static inline void wq_list_add_after(struct io_wq_work_node *node,
 				     struct io_wq_work_node *pos,
 				     struct io_wq_work_list *list)
-- 
2.36.0