[PATCH 1/2] Remove preempt_enable/disable calls around sched_clock()

[PATCH 1/2] Remove preempt_enable/disable calls around sched_clock()

[Divyesh Shah]

calls in the block layer. This was a temporary fix added.

Signed-off-by: Divyesh Shah <dpshah@google.com>
---
 include/linux/blkdev.h |    4 ----
 1 files changed, 0 insertions(+), 4 deletions(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 09a8402..ebe788e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1218,16 +1218,12 @@ int kblockd_schedule_work(struct request_queue *q, struct work_struct *work);
  */
 static inline void set_start_time_ns(struct request *req)
 {
-	preempt_disable();
 	req->start_time_ns = sched_clock();
-	preempt_enable();
 }
 
 static inline void set_io_start_time_ns(struct request *req)
 {
-	preempt_disable();
 	req->io_start_time_ns = sched_clock();
-	preempt_enable();
 }
 
 static inline uint64_t rq_start_time_ns(struct request *req)

[PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio cgroup stats.

[Divyesh Shah]

This will take care of the pre-emptive kernel issue and the unbounded
TSC drift problem. We will lose resolution though in some cases.

Signed-off-by: Divyesh Shah <dpshah@google.com>
---
 block/blk-cgroup.c     |   22 +++++++++++-----------
 include/linux/blkdev.h |    4 ++--
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a680964..711766d 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -135,19 +135,19 @@ static void blkio_set_start_group_wait_time(struct blkio_group *blkg,
 		return;
 	if (blkg == curr_blkg)
 		return;
-	blkg->stats.start_group_wait_time = sched_clock();
+	blkg->stats.start_group_wait_time = ktime_to_ns(ktime_get());
 	blkio_mark_blkg_waiting(&blkg->stats);
 }
 
 /* This should be called with the blkg->stats_lock held. */
 static void blkio_update_group_wait_time(struct blkio_group_stats *stats)
 {
-	unsigned long long now;
+	u64 now;
 
 	if (!blkio_blkg_waiting(stats))
 		return;
 
-	now = sched_clock();
+	now = ktime_to_ns(ktime_get());
 	if (time_after64(now, stats->start_group_wait_time))
 		stats->group_wait_time += now - stats->start_group_wait_time;
 	blkio_clear_blkg_waiting(stats);
@@ -156,12 +156,12 @@ static void blkio_update_group_wait_time(struct blkio_group_stats *stats)
 /* This should be called with the blkg->stats_lock held. */
 static void blkio_end_empty_time(struct blkio_group_stats *stats)
 {
-	unsigned long long now;
+	u64 now;
 
 	if (!blkio_blkg_empty(stats))
 		return;
 
-	now = sched_clock();
+	now = ktime_to_ns(ktime_get());
 	if (time_after64(now, stats->start_empty_time))
 		stats->empty_time += now - stats->start_empty_time;
 	blkio_clear_blkg_empty(stats);
@@ -173,7 +173,7 @@ void blkiocg_update_set_idle_time_stats(struct blkio_group *blkg)
 
 	spin_lock_irqsave(&blkg->stats_lock, flags);
 	BUG_ON(blkio_blkg_idling(&blkg->stats));
-	blkg->stats.start_idle_time = sched_clock();
+	blkg->stats.start_idle_time = ktime_to_ns(ktime_get());
 	blkio_mark_blkg_idling(&blkg->stats);
 	spin_unlock_irqrestore(&blkg->stats_lock, flags);
 }
@@ -182,13 +182,13 @@ EXPORT_SYMBOL_GPL(blkiocg_update_set_idle_time_stats);
 void blkiocg_update_idle_time_stats(struct blkio_group *blkg)
 {
 	unsigned long flags;
-	unsigned long long now;
+	u64 now;
 	struct blkio_group_stats *stats;
 
 	spin_lock_irqsave(&blkg->stats_lock, flags);
 	stats = &blkg->stats;
 	if (blkio_blkg_idling(stats)) {
-		now = sched_clock();
+		now = ktime_to_ns(ktime_get());
 		if (time_after64(now, stats->start_idle_time))
 			stats->idle_time += now - stats->start_idle_time;
 		blkio_clear_blkg_idling(stats);
@@ -237,7 +237,7 @@ void blkiocg_set_start_empty_time(struct blkio_group *blkg)
 		return;
 	}
 
-	stats->start_empty_time = sched_clock();
+	stats->start_empty_time = ktime_to_ns(ktime_get());
 	blkio_mark_blkg_empty(stats);
 	spin_unlock_irqrestore(&blkg->stats_lock, flags);
 }
@@ -314,7 +314,7 @@ void blkiocg_update_completion_stats(struct blkio_group *blkg,
 {
 	struct blkio_group_stats *stats;
 	unsigned long flags;
-	unsigned long long now = sched_clock();
+	u64 now = ktime_to_ns(ktime_get());
 
 	spin_lock_irqsave(&blkg->stats_lock, flags);
 	stats = &blkg->stats;
@@ -464,7 +464,7 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
 	int i;
 #ifdef CONFIG_DEBUG_BLK_CGROUP
 	bool idling, waiting, empty;
-	unsigned long long now = sched_clock();
+	u64 now = ktime_to_ns(ktime_get());
 #endif
 
 	blkcg = cgroup_to_blkio_cgroup(cgroup);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ebe788e..f174b34 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1218,12 +1218,12 @@ int kblockd_schedule_work(struct request_queue *q, struct work_struct *work);
  */
 static inline void set_start_time_ns(struct request *req)
 {
-	req->start_time_ns = sched_clock();
+	req->start_time_ns = ktime_to_ns(ktime_get());
 }
 
 static inline void set_io_start_time_ns(struct request *req)
 {
-	req->io_start_time_ns = sched_clock();
+	req->io_start_time_ns = ktime_to_ns(ktime_get());
 }
 
 static inline uint64_t rq_start_time_ns(struct request *req)

Re: [PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio cgroup stats.

[Ingo Molnar]

* Divyesh Shah <dpshah@google.com> wrote:

> This will take care of the pre-emptive kernel issue and the unbounded
> TSC drift problem. We will lose resolution though in some cases.

> -	blkg->stats.start_group_wait_time = sched_clock();
> +	blkg->stats.start_group_wait_time = ktime_to_ns(ktime_get());

Ugh!

ktime_get() can have insanely high overhead. Peter has added local_clock(), if 
then you should use that and apply checks to make sure the result isnt 
negative.

	Ingo

Re: [PATCH 1/2] Remove preempt_enable/disable calls around sched_clock()

[Ingo Molnar]

* Divyesh Shah <dpshah@google.com> wrote:

> calls in the block layer. This was a temporary fix added.

Not good, this commit reintroduces those ugly warnings, if someone happens to 
bisect straight into this commit.

	Ingo

Re: [PATCH 2/2] Use ktime_get() instead of sched_clock() for blkio cgroup stats.

[Divyesh Shah]

On Sat, Jun 12, 2010 at 12:18 AM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Divyesh Shah <dpshah@google.com> wrote:
>
>> This will take care of the pre-emptive kernel issue and the unbounded
>> TSC drift problem. We will lose resolution though in some cases.
>
>> -     blkg->stats.start_group_wait_time = sched_clock();
>> +     blkg->stats.start_group_wait_time = ktime_to_ns(ktime_get());
>
> Ugh!
>
> ktime_get() can have insanely high overhead. Peter has added local_clock(), if
> then you should use that and apply checks to make sure the result isnt
> negative.

Ok. The negative checks are already in the code.

>
>        Ingo
>

Re: [PATCH 1/2] Remove preempt_enable/disable calls around sched_clock()

[Divyesh Shah]

On Sat, Jun 12, 2010 at 12:19 AM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Divyesh Shah <dpshah@google.com> wrote:
>
>> calls in the block layer. This was a temporary fix added.
>
> Not good, this commit reintroduces those ugly warnings, if someone happens to
> bisect straight into this commit.

You're right. In the next version, I'll merge both patches into one so
this cannot happen.

>
>        Ingo
>

Re: [PATCH 1/2] Remove preempt_enable/disable calls around sched_clock()

[Ingo Molnar]

* Divyesh Shah <dpshah@google.com> wrote:

> On Sat, Jun 12, 2010 at 12:19 AM, Ingo Molnar <mingo@elte.hu> wrote:
> >
> > * Divyesh Shah <dpshah@google.com> wrote:
> >
> >> calls in the block layer. This was a temporary fix added.
> >
> > Not good, this commit reintroduces those ugly warnings, if someone happens to
> > bisect straight into this commit.
> 
> You're right. In the next version, I'll merge both patches into one so
> this cannot happen.

Yeah - or if you really want to make a point of doing the two things in two 
separate patches you can first fix the API, _then_ remove the preemption 
enable/disable.

Thanks,

	Ingo