[SRU][Bionic][PATCH] sched/fair: Fix -Wunused-but-set-variable warnings

[Juerg Haefliger]

From: Qian Cai <cai at lca.pw>

BugLink: https://bugs.launchpad.net/bugs/1832151

Commit:

   de53fd7aedb1 ("sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices")

introduced a few compilation warnings:

  kernel/sched/fair.c: In function '__refill_cfs_bandwidth_runtime':
  kernel/sched/fair.c:4365:6: warning: variable 'now' set but not used [-Wunused-but-set-variable]
  kernel/sched/fair.c: In function 'start_cfs_bandwidth':
  kernel/sched/fair.c:4992:6: warning: variable 'overrun' set but not used [-Wunused-but-set-variable]

Also, __refill_cfs_bandwidth_runtime() does no longer update the
expiration time, so fix the comments accordingly.

Signed-off-by: Qian Cai <cai at lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Reviewed-by: Ben Segall <bsegall at google.com>
Reviewed-by: Dave Chiluk <chiluk+linux at indeed.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: pauld at redhat.com
Fixes: de53fd7aedb1 ("sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices")
Link: https://lkml.kernel.org/r/1566326455-8038-1-git-send-email-cai@lca.pw
Signed-off-by: Ingo Molnar <mingo at kernel.org>
(backported from commit 763a9ec06c409dcde2a761aac4bb83ff3938e0b3)
[juergh: Dropped modifications of start_cfs_bandwidth() (not applicable for
 Bionic 4.15).]
Signed-off-by: Juerg Haefliger <juergh at canonical.com>
---
 kernel/sched/fair.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7c797c8c8071..6c5766f9e924 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4429,21 +4429,16 @@ static inline u64 sched_cfs_bandwidth_slice(void)
 }
 
 /*
- * Replenish runtime according to assigned quota and update expiration time.
- * We use sched_clock_cpu directly instead of rq->clock to avoid adding
- * additional synchronization around rq->lock.
+ * Replenish runtime according to assigned quota. We use sched_clock_cpu
+ * directly instead of rq->clock to avoid adding additional synchronization
+ * around rq->lock.
  *
  * requires cfs_b->lock
  */
 void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
 {
-	u64 now;
-
-	if (cfs_b->quota == RUNTIME_INF)
-		return;
-
-	now = sched_clock_cpu(smp_processor_id());
-	cfs_b->runtime = cfs_b->quota;
+	if (cfs_b->quota != RUNTIME_INF)
+		cfs_b->runtime = cfs_b->quota;
 }
 
 static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
-- 
2.20.1