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[188.28.109.17]) by smtp.gmail.com with ESMTPSA id m22-20020a05600c3b1600b003cfd4cf0761sm27067165wms.1.2022.12.20.09.59.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Dec 2022 09:59:39 -0800 (PST) From: Pavel Begunkov To: io-uring@vger.kernel.org Cc: Jens Axboe , asml.silence@gmail.com Subject: [RFC] io_uring: wake up optimisations Date: Tue, 20 Dec 2022 17:58:28 +0000 Message-Id: <81104db1a04efbfcec90f5819081b4299542671a.1671559005.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.38.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 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 --- 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);