The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 7b72d661f1f2f950ab8c12de7e2bc48bdac8ed69 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023080154-handed-folic-f52f@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
Possible dependencies:
7b72d661f1f2 ("io_uring: gate iowait schedule on having pending requests") 8a796565cec3 ("io_uring: Use io_schedule* in cqring wait") d33a39e57768 ("io_uring: keep timeout in io_wait_queue") 46ae7eef44f6 ("io_uring: optimise non-timeout waiting") 846072f16eed ("io_uring: mimimise io_cqring_wait_schedule") 3fcf19d592d5 ("io_uring: parse check_cq out of wq waiting") 12521a5d5cb7 ("io_uring: fix CQ waiting timeout handling") 52ea806ad983 ("io_uring: finish waiting before flushing overflow entries") 35d90f95cfa7 ("io_uring: include task_work run after scheduling in wait for events") 1b346e4aa8e7 ("io_uring: don't check overflow flush failures") a85381d8326d ("io_uring: skip overflow CQE posting for dying ring") c0e0d6ba25f1 ("io_uring: add IORING_SETUP_DEFER_TASKRUN") b4c98d59a787 ("io_uring: introduce io_has_work") 78a861b94959 ("io_uring: add sync cancelation API through io_uring_register()") c34398a8c018 ("io_uring: remove __io_req_task_work_add") ed5ccb3beeba ("io_uring: remove priority tw list optimisation") 4a0fef62788b ("io_uring: optimize io_uring_task layout") 253993210bd8 ("io_uring: introduce locking helpers for CQE posting") 305bef988708 ("io_uring: hide eventfd assumptions in eventfd paths") affa87db9010 ("io_uring: fix multi ctx cancellation")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 7b72d661f1f2f950ab8c12de7e2bc48bdac8ed69 Mon Sep 17 00:00:00 2001 From: Jens Axboe axboe@kernel.dk Date: Mon, 24 Jul 2023 11:28:17 -0600 Subject: [PATCH] io_uring: gate iowait schedule on having pending requests
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@vger.kernel.org Link: https://lore.kernel.org/io-uring/CAMEGJJ2RxopfNQ7GNLhr7X9=bHXKo+G5OOe0LUq=+U... 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@natalenko.name Reported-by: Phil Elwell phil@raspberrypi.com Tested-by: Andres Freund andres@anarazel.de Fixes: 8a796565cec3 ("io_uring: Use io_schedule* in cqring wait") Signed-off-by: Jens Axboe axboe@kernel.dk
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; }