Commit 06cceedc authored Mar 27, 2017 by Shaohua Li Committed by Jens Axboe Mar 28, 2017

blk-throttle: make sure expire time isn't too big

cgroup could be throttled to a limit but when all cgroups cross high
limit, queue enters a higher state and so the group should be throttled
to a higher limit. It's possible the cgroup is sleeping because of
throttle and other cgroups don't dispatch IO any more. In this case,
nobody can trigger current downgrade/upgrade logic. To fix this issue,
we could either set up a timer to wakeup the cgroup if other cgroups are
idle or make sure this cgroup doesn't sleep too long. Setting up a timer
means we must change the timer very frequently. This patch chooses the
latter. Making cgroup sleep time not too big wouldn't change cgroup
bps/iops, but could make it wakeup more frequently, which isn't a big
issue because throtl_slice * 8 is already quite big.

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 3f0abd80

block/blk-throttle.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -590,6 +590,17 @@ static void throtl_dequeue_tg(struct throtl_grp *tg)
		static void throtl_schedule_pending_timer(struct throtl_service_queue *sq,
		unsigned long expires)
		{
		unsigned long max_expire = jiffies + 8 * throtl_slice;

		/*
		* Since we are adjusting the throttle limit dynamically, the sleep
		* time calculated according to previous limit might be invalid. It's
		* possible the cgroup sleep time is very long and no other cgroups
		* have IO running so notify the limit changes. Make sure the cgroup
		* doesn't sleep too long to avoid the missed notification.
		*/
		if (time_after(expires, max_expire))
		expires = max_expire;
		mod_timer(&sq->pending_timer, expires);
		throtl_log(sq, "schedule timer. delay=%lu jiffies=%lu",
		expires - jiffies, jiffies);

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