From 6a525600ffeb9e0d6cbbebda49eb89d6d3408c2b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 14 May 2013 13:52:32 -0700 Subject: blk-throttle: remove pointless throtl_nr_queued() optimizations 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 Acked-by: Vivek Goyal --- block/blk-throttle.c | 29 +++++++---------------------- 1 file changed, 7 insertions(+), 22 deletions(-) (limited to 'block') diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 507b1c6..dbeef30 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -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); - } + mod_delayed_work(kthrotld_workqueue, dwork, delay); + 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); /* -- cgit v1.1