blk-throttle: remove pointless throtl_nr_queued() optimizations (6a525600) · Commits · 戴 / test

throtl_nr_queued() is used in several places to avoid performing certain operations when the throtl_data is empty. This usually is useless as those paths usually aren't traveled if there's no bio queued. * throtl_schedule_delayed_work() skips scheduling dispatch work item if @td doesn't have any bios queued; however, the only case it can be called when @td is empty is from tg_set_conf() which isn't something we should be optimizing for. * throtl_schedule_next_dispatch() takes a quick exit if @td is empty; however, right after that it triggers BUG if the service tree is empty. The two conditions are equivalent and it can just test @st->count for the quick exit. * blk_throtl_dispatch_work_fn() skips dispatch if @td is empty. This work function isn't usually invoked when @td is empty. The only possibility is from tg_set_conf() and when it happens the normal dispatching path can handle empty @td fine. No need to add special skip path. This patch removes the above three unnecessary optimizations, which leave throtl_log() call in blk_throtl_dispatch_work_fn() the only user of throtl_nr_queued(). Remove throtl_nr_queued() and open code it in throtl_log(). I don't think we need td->nr_queued[] at all. Maybe we can remove it later. Signed-off-by:

Tejun Heo <tj@kernel.org> Acked-by:

Vivek Goyal <vgoyal@redhat.com>

block/blk-throttle.c

+7 −22

Original line number	Diff line number	Diff line
		@@ -166,11 +166,6 @@ THROTL_TG_FNS(on_rr);
		#define throtl_log(td, fmt, args...) \
		blk_add_trace_msg((td)->queue, "throtl " fmt, ##args)

		static inline unsigned int total_nr_queued(struct throtl_data *td)
		{
		return td->nr_queued[0] + td->nr_queued[1];
		}

		/*
		* Worker for allocating per cpu stat for tgs. This is scheduled on the
		* system_wq once there are some groups on the alloc_list waiting for
		@@ -402,25 +397,18 @@ static void throtl_schedule_delayed_work(struct throtl_data *td,
		{
		struct delayed_work *dwork = &td->dispatch_work;

		if (total_nr_queued(td)) {
		mod_delayed_work(kthrotld_workqueue, dwork, delay);
		throtl_log(td, "schedule work. delay=%lu jiffies=%lu",
		delay, jiffies);
		}
		throtl_log(td, "schedule work. delay=%lu jiffies=%lu", delay, jiffies);
		}

		static void throtl_schedule_next_dispatch(struct throtl_data *td)
		{
		struct throtl_rb_root *st = &td->tg_service_tree;

		/*
		* If there are more bios pending, schedule more work.
		*/
		if (!total_nr_queued(td))
		/* any pending children left? */
		if (!st->count)
		return;

		BUG_ON(!st->count);

		update_min_dispatch_time(st);

		if (time_before_eq(st->min_disptime, jiffies))
		@@ -844,14 +832,11 @@ void blk_throtl_dispatch_work_fn(struct work_struct *work)

		spin_lock_irq(q->queue_lock);

		if (!total_nr_queued(td))
		goto out;

		bio_list_init(&bio_list_on_stack);

		throtl_log(td, "dispatch nr_queued=%u read=%u write=%u",
		total_nr_queued(td), td->nr_queued[READ],
		td->nr_queued[WRITE]);
		td->nr_queued[READ] + td->nr_queued[WRITE],
		td->nr_queued[READ], td->nr_queued[WRITE]);

		nr_disp = throtl_select_dispatch(td, &bio_list_on_stack);

		@@ -859,7 +844,7 @@ void blk_throtl_dispatch_work_fn(struct work_struct *work)
		throtl_log(td, "bios disp=%u", nr_disp);

		throtl_schedule_next_dispatch(td);
		out:

		spin_unlock_irq(q->queue_lock);

		/*

Admin message