From: Pavel Begunkov <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>, [email protected]
Subject: [RFC] io_uring: wake up optimisations
Date: Tue, 20 Dec 2022 17:58:28 +0000 [thread overview]
Message-ID: <81104db1a04efbfcec90f5819081b4299542671a.1671559005.git.asml.silence@gmail.com> (raw)
NOT FOR INCLUSION, needs some ring poll workarounds
Flush completions is done either from the submit syscall or by the
task_work, both are in the context of the submitter task, and when it
goes for a single threaded rings like implied by ->task_complete, there
won't be any waiters on ->cq_wait but the master task. That means that
there can be no tasks sleeping on cq_wait while we run
__io_submit_flush_completions() and so waking up can be skipped.
Signed-off-by: Pavel Begunkov <[email protected]>
---
io_uring/io_uring.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 16a323a9ff70..a57b9008807c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -618,6 +618,25 @@ static inline void __io_cq_unlock_post(struct io_ring_ctx *ctx)
io_cqring_wake(ctx);
}
+static inline void __io_cq_unlock_post_flush(struct io_ring_ctx *ctx)
+ __releases(ctx->completion_lock)
+{
+ io_commit_cqring(ctx);
+ __io_cq_unlock(ctx);
+ io_commit_cqring_flush(ctx);
+
+ /*
+ * As ->task_complete implies that the ring is single tasked, cq_wait
+ * may only be waited on by the current in io_cqring_wait(), but since
+ * it will re-check the wakeup conditions once we return we can safely
+ * skip waking it up.
+ */
+ if (!ctx->task_complete) {
+ smp_mb();
+ __io_cqring_wake(ctx);
+ }
+}
+
void io_cq_unlock_post(struct io_ring_ctx *ctx)
__releases(ctx->completion_lock)
{
@@ -1458,7 +1477,7 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
}
}
}
- __io_cq_unlock_post(ctx);
+ __io_cq_unlock_post_flush(ctx);
if (!wq_list_empty(&ctx->submit_state.compl_reqs)) {
io_free_batch_list(ctx, state->compl_reqs.first);
--
2.38.1
next reply other threads:[~2022-12-20 17:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-20 17:58 Pavel Begunkov [this message]
2022-12-20 18:06 ` [RFC] io_uring: wake up optimisations Pavel Begunkov
2022-12-20 18:10 ` Jens Axboe
2022-12-20 19:12 ` Pavel Begunkov
2022-12-20 19:22 ` Jens Axboe
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