[PATCH v2] blk-iolatency: postpone ktime_get() execution until blk_iolatency_enabled() return true

[PATCH v2] blk-iolatency: postpone ktime_get() execution until blk_iolatency_enabled() return true

[Hongnan Li]

ktime_to_ns(ktime_get()) which is expensive do not need to be executed if
blk_iolatency_enabled() return false in blkcg_iolatency_done_bio().
Postponing ktime_to_ns(ktime_get()) execution can reduce CPU usage
when blk_iolatency was disabled.

---
V2:
  1.Fix compile warnings.

Signed-off-by: Hongnan Li <hongnan.li@linux.alibaba.com>
---
 block/blk-iolatency.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index c128d50..f90429c 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -591,7 +591,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
 	struct rq_wait *rqw;
 	struct iolatency_grp *iolat;
 	u64 window_start;
-	u64 now = ktime_to_ns(ktime_get());
+	u64 now;
 	bool issue_as_root = bio_issue_as_root_blkg(bio);
 	bool enabled = false;
 	int inflight = 0;
@@ -608,6 +608,7 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
 	if (!enabled)
 		return;
 
+	now = ktime_to_ns(ktime_get());
 	while (blkg && blkg->parent) {
 		iolat = blkg_to_lat(blkg);
 		if (!iolat) {
-- 
1.8.3.1

Re: [PATCH v2] blk-iolatency: postpone ktime_get() execution until blk_iolatency_enabled() return true

[Jens Axboe]

On 7/1/20 2:09 AM, Hongnan Li wrote:
> ktime_to_ns(ktime_get()) which is expensive do not need to be executed if
> blk_iolatency_enabled() return false in blkcg_iolatency_done_bio().
> Postponing ktime_to_ns(ktime_get()) execution can reduce CPU usage
> when blk_iolatency was disabled.
> 
> ---
> V2:
>   1.Fix compile warnings.
> 
> Signed-off-by: Hongnan Li <hongnan.li@linux.alibaba.com>

I've applied this (rewrote header+commit message somewhat). But a note for the
future - anything below the first --- is removed, so you'll need to put your
SOB right below the commit message. And the v2 etc info should go here:

> ---
>  block/blk-iolatency.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

instead of having two --- sections.

-- 
Jens Axboe