io_uring: include task_work run after scheduling in wait for events

It's quite possible that we got woken up because task_work was queued,
and we need to process this task_work to generate the events waited for.
If we return to the wait loop without running task_work, we'll end up
adding the task to the waitqueue again, only to call
io_cqring_wait_schedule() again which will run the task_work. This is
less efficient than it could be, as it requires adding to the cq_wait
queue again. It also triggers the wakeup path for completions as
cq_wait is now non-empty with the task itself, and it'll require another
lock grab and deletion to remove ourselves from the waitqueue.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 16a323a..ff2bbac 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2481,7 +2481,14 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
        }
        if (!schedule_hrtimeout(&timeout, HRTIMER_MODE_ABS))
                return -ETIME;
-       return 1;
+
+       /*
+        * Run task_work after scheduling. If we got woken because of
+        * task_work being processed, run it now rather than let the caller
+        * do another wait loop.
+        */
+       ret = io_run_task_work_sig(ctx);
+       return ret < 0 ? ret : 1;
 }
 
 /*
@@ -2546,6 +2553,8 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
                prepare_to_wait_exclusive(&ctx->cq_wait, &iowq.wq,
                                                TASK_INTERRUPTIBLE);
                ret = io_cqring_wait_schedule(ctx, &iowq, timeout);
+               if (__io_cqring_events_user(ctx) >= min_events)
+                       break;
                cond_resched();
        } while (ret > 0);