[PATCH v2 1/9] io_uring: optimise iowq refcounting

Pavel Begunkov
2021-08-15T09:41:06Z

If a requests is forwarded into io-wq, there is a good chance it hasn't
been refcounted yet and we can save one req_ref_get() by setting the
refcount number to the right value directly.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/io_uring.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 51c4166f68b5..761bfb56ed3b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1115,14 +1115,19 @@ static inline void req_ref_get(struct io_kiocb *req)
atomic_inc(&req->refs);
}

-static inline void io_req_refcount(struct io_kiocb *req)
+static inline void __io_req_set_refcount(struct io_kiocb *req, int nr)
{
if (!(req->flags & REQ_F_REFCOUNT)) {
req->flags |= REQ_F_REFCOUNT;
- atomic_set(&req->refs, 1);
+ atomic_set(&req->refs, nr);
}
}

+static inline void io_req_set_refcount(struct io_kiocb *req)
+{
+ __io_req_set_refcount(req, 1);
+}
+
static inline void io_req_set_rsrc_node(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
@@ -1304,8 +1309,8 @@ static struct io_kiocb *__io_prep_linked_timeout(struct io_kiocb *req)
return NULL;

/* linked timeouts should have two refs once prep'ed */
- io_req_refcount(req);
- io_req_refcount(nxt);
+ io_req_set_refcount(req);
+ io_req_set_refcount(nxt);
req_ref_get(nxt);

nxt->timeout.head = req;
@@ -5231,7 +5236,7 @@ static int io_arm_poll_handler(struct io_kiocb *req)
req->apoll = apoll;
req->flags |= REQ_F_POLLED;
ipt.pt._qproc = io_async_queue_proc;
- io_req_refcount(req);
+ io_req_set_refcount(req);

ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
io_async_wake);
@@ -5419,7 +5424,7 @@ static int io_poll_add_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe
if (flags & ~IORING_POLL_ADD_MULTI)
return -EINVAL;

- io_req_refcount(req);
+ io_req_set_refcount(req);
poll->events = io_poll_parse_events(sqe, flags);
return 0;
}
@@ -6311,9 +6316,11 @@ static void io_wq_submit_work(struct io_wq_work *work)
struct io_kiocb *timeout;
int ret = 0;

- io_req_refcount(req);
- /* will be dropped by ->io_free_work() after returning to io-wq */
- req_ref_get(req);
+ /* one will be dropped by ->io_free_work() after returning to io-wq */
+ if (!(req->flags & REQ_F_REFCOUNT))
+ __io_req_set_refcount(req, 2);
+ else
+ req_ref_get(req);

timeout = io_prep_linked_timeout(req);
if (timeout)
--
2.32.0