linux-kernel - [GIT PULL] scheduler fixes

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Date:   Sat, 12 Oct 2019 16:58:36 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: [GIT PULL] scheduler fixes

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

   # HEAD: 68e7a4d66b0ce04bf18ff2ffded5596ab3618585 sched/vtime: Fix guest/system mis-accounting on task switch

Two fixes: a guest-cputime accounting fix, and a cgroup bandwidth quota 
precision fix.

 Thanks,

	Ingo

------------------>
Frederic Weisbecker (1):
      sched/vtime: Fix guest/system mis-accounting on task switch

Xuewei Zhang (1):
      sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision


 kernel/sched/cputime.c |  6 +++---
 kernel/sched/fair.c    | 36 ++++++++++++++++++++++--------------
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 2305ce89a26c..46ed4e1383e2 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -740,7 +740,7 @@ void vtime_account_system(struct task_struct *tsk)
 
 	write_seqcount_begin(&vtime->seqcount);
 	/* We might have scheduled out from guest path */
-	if (current->flags & PF_VCPU)
+	if (tsk->flags & PF_VCPU)
 		vtime_account_guest(tsk, vtime);
 	else
 		__vtime_account_system(tsk, vtime);
@@ -783,7 +783,7 @@ void vtime_guest_enter(struct task_struct *tsk)
 	 */
 	write_seqcount_begin(&vtime->seqcount);
 	__vtime_account_system(tsk, vtime);
-	current->flags |= PF_VCPU;
+	tsk->flags |= PF_VCPU;
 	write_seqcount_end(&vtime->seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_enter);
@@ -794,7 +794,7 @@ void vtime_guest_exit(struct task_struct *tsk)
 
 	write_seqcount_begin(&vtime->seqcount);
 	vtime_account_guest(tsk, vtime);
-	current->flags &= ~PF_VCPU;
+	tsk->flags &= ~PF_VCPU;
 	write_seqcount_end(&vtime->seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_exit);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 83ab35e2374f..682a754ea3e1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4926,20 +4926,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 		if (++count > 3) {
 			u64 new, old = ktime_to_ns(cfs_b->period);
 
-			new = (old * 147) / 128; /* ~115% */
-			new = min(new, max_cfs_quota_period);
-
-			cfs_b->period = ns_to_ktime(new);
-
-			/* since max is 1s, this is limited to 1e9^2, which fits in u64 */
-			cfs_b->quota *= new;
-			cfs_b->quota = div64_u64(cfs_b->quota, old);
-
-			pr_warn_ratelimited(
-	"cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n",
-				smp_processor_id(),
-				div_u64(new, NSEC_PER_USEC),
-				div_u64(cfs_b->quota, NSEC_PER_USEC));
+			/*
+			 * Grow period by a factor of 2 to avoid losing precision.
+			 * Precision loss in the quota/period ratio can cause __cfs_schedulable
+			 * to fail.
+			 */
+			new = old * 2;
+			if (new < max_cfs_quota_period) {
+				cfs_b->period = ns_to_ktime(new);
+				cfs_b->quota *= 2;
+
+				pr_warn_ratelimited(
+	"cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us = %lld, cfs_quota_us = %lld)\n",
+					smp_processor_id(),
+					div_u64(new, NSEC_PER_USEC),
+					div_u64(cfs_b->quota, NSEC_PER_USEC));
+			} else {
+				pr_warn_ratelimited(
+	"cfs_period_timer[cpu%d]: period too short, but cannot scale up without losing precision (cfs_period_us = %lld, cfs_quota_us = %lld)\n",
+					smp_processor_id(),
+					div_u64(old, NSEC_PER_USEC),
+					div_u64(cfs_b->quota, NSEC_PER_USEC));
+			}
 
 			/* reset count so we don't come right back in here */
 			count = 0;