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authorTejun Heo <tj@kernel.org>2013-05-14 13:52:32 -0700
committerTejun Heo <tj@kernel.org>2013-05-14 13:52:32 -0700
commit6a525600ffeb9e0d6cbbebda49eb89d6d3408c2b (patch)
treef4ced3b39162c54ecf12f0171b781e60d54e4a7c /block
parenta9131a27e2a3272df2207277a2be90377ce75fc6 (diff)
downloadlinux-6a525600ffeb9e0d6cbbebda49eb89d6d3408c2b.tar.bz2
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 <tj@kernel.org> Acked-by: Vivek Goyal <vgoyal@redhat.com>
Diffstat (limited to 'block')
-rw-r--r--block/blk-throttle.c29
1 files changed, 7 insertions, 22 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 507b1c608941..dbeef303f27b 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);
/*