linux-kernel - [PATCH 7/9] io-wq: io_worker_handle

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Message-Id: <36973f2a05ff0f8e955113e0a14c83a425ee6498.1583078091.git.asml.silence@gmail.com>
Date:   Sun,  1 Mar 2020 19:18:24 +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 7/9] io-wq: io_worker_handle_work() optimise locking

There are 2 points:
- dependant requests are not hashed, don't lock &wqe->lock for them
- remove extra spin_lock_irq(&worker->lock) to reset worker->cur_work
to NULL, because it will be set to a dependant request in a moment.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 fs/io-wq.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 3a97d35b569e..da67c931db79 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -476,9 +476,8 @@ static void io_worker_handle_work(struct io_worker *worker)
 	struct io_wq *wq = wqe->wq;
 
 	do {
-		struct io_wq_work *work, *old_work;
+		struct io_wq_work *work;
 		unsigned hash = -1U;
-		bool is_internal;
 
 		/*
 		 * If we got some work, mark us as busy. If we didn't, but
@@ -496,12 +495,14 @@ static void io_worker_handle_work(struct io_worker *worker)
 		spin_unlock_irq(&wqe->lock);
 		if (!work)
 			break;
+		io_assign_current_work(worker, work);
 
 		/* handle a whole dependent link */
 		do {
-			io_assign_current_work(worker, work);
-			io_impersonate_work(worker, work);
+			bool is_internal;
+			struct io_wq_work *old_work;
 
+			io_impersonate_work(worker, work);
 			/*
 			 * OK to set IO_WQ_WORK_CANCEL even for uncancellable
 			 * work, the worker function will do the right thing.
@@ -515,10 +516,8 @@ static void io_worker_handle_work(struct io_worker *worker)
 
 			old_work = work;
 			work->func(&work);
-
-			spin_lock_irq(&worker->lock);
-			worker->cur_work = NULL;
-			spin_unlock_irq(&worker->lock);
+			work = (old_work == work) ? NULL : work;
+			io_assign_current_work(worker, work);
 
 			if (wq->put_work && !is_internal)
 				wq->put_work(old_work);
@@ -527,11 +526,11 @@ static void io_worker_handle_work(struct io_worker *worker)
 				spin_lock_irq(&wqe->lock);
 				wqe->hash_map &= ~BIT_ULL(hash);
 				wqe->flags &= ~IO_WQE_FLAG_STALLED;
-				spin_unlock_irq(&wqe->lock);
 				/* dependent work is not hashed */
 				hash = -1U;
+				spin_unlock_irq(&wqe->lock);
 			}
-		} while (work && work != old_work);
+		} while (work);
 
 		spin_lock_irq(&wqe->lock);
 	} while (1);
-- 
2.24.0