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


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