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Subject[PATCH 7/9] io-wq: io_worker_handle_work() optimise locking
Date
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@gmail.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
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