From: Hongnan Li <hongnan.li@linux.alibaba.com>
Date: Wed, 1 Jul 2020 16:09:38 +0800
Subject: [PATCH] blk-iolatency: only call ktime_get() if needed
References: bsc#1175995,jsc#SLE-15608
Git-commit: 6e2fa4dd683a22a7697e7ff51dad499406094d28
Patch-mainline: v5.9-rc1

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>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 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 c128d50cb410..f90429cf4edf 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) {
-- 
2.16.4