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blk-iolatency: only call ktime_get() if needed 

ktime_to_ns(ktime_get()), which is expensive, does not need to be called
if blk_iolatency_enabled() return false in blkcg_iolatency_done_bio().
Postponing ktime_to_ns(ktime_get()) execution reduces the CPU usage when
blk_iolatency is disabled.

Signed-off-by: Hongnan Li <hongnan.li@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Hongnan Li 2020-07-01 16:09:38 +08:00 committed by Jens Axboe
parent 5a6c35f9af
commit 6e2fa4dd68
1 changed files with 2 additions and 1 deletions
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3
block/blk-iolatency.c
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@ -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) {