A previous commit made all cqring waits marked as iowait, as a way to improve performance for short schedules with pending IO. However, for use cases that have a special reaper thread that does nothing but wait on events on the ring, this causes a cosmetic issue where we know have one core marked as being "busy" with 100% iowait. While this isn't a grave issue, it is confusing to users. Rather than always mark us as being in iowait, gate setting of current->in_iowait to 1 by whether or not the waiting task has pending requests. Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/io-uring/CAMEGJJ2RxopfNQ7GNLhr7X9=bHXKo+G5OOe0LUq=+UgLXsv1Xg@xxxxxxxxxxxxxx/ Link: https://bugzilla.kernel.org/show_bug.cgi?id=217699 Link: https://bugzilla.kernel.org/show_bug.cgi?id=217700 Reported-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> Reported-by: Phil Elwell <phil@xxxxxxxxxxxxxxx> Tested-by: Andres Freund <andres@xxxxxxxxxxx> Fixes: 8a796565cec3 ("io_uring: Use io_schedule* in cqring wait") Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 89a611541bc4..f4591b912ea8 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2493,11 +2493,20 @@ int io_run_task_work_sig(struct io_ring_ctx *ctx) return 0; } +static bool current_pending_io(void) +{ + struct io_uring_task *tctx = current->io_uring; + + if (!tctx) + return false; + return percpu_counter_read_positive(&tctx->inflight); +} + /* when returns >0, the caller should retry */ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, struct io_wait_queue *iowq) { - int token, ret; + int io_wait, ret; if (unlikely(READ_ONCE(ctx->check_cq))) return 1; @@ -2511,17 +2520,19 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx, return 0; /* - * Use io_schedule_prepare/finish, so cpufreq can take into account - * that the task is waiting for IO - turns out to be important for low - * QD IO. + * Mark us as being in io_wait if we have pending requests, so cpufreq + * can take into account that the task is waiting for IO - turns out + * to be important for low QD IO. */ - token = io_schedule_prepare(); + io_wait = current->in_iowait; + if (current_pending_io()) + current->in_iowait = 1; ret = 0; if (iowq->timeout == KTIME_MAX) schedule(); else if (!schedule_hrtimeout(&iowq->timeout, HRTIMER_MODE_ABS)) ret = -ETIME; - io_schedule_finish(token); + current->in_iowait = io_wait; return ret; } -- Jens Axboe
