From: Liangyan <liangyan.peng@linux.alibaba.com>
To: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Ben Segall <bsegall@google.com>,
Valentin Schneider <valentin.schneider@arm.com>,
linux-kernel@vger.kernel.org
Cc: shanpeic@linux.alibaba.com, xlpang@linux.alibaba.com
Subject: [PATCH v2] sched/fair: don't assign runtime for throttled cfs_rq
Date: Sat, 24 Aug 2019 17:15:58 +0800 [thread overview]
Message-ID: <20190824091558.86296-1-liangyan.peng@linux.alibaba.com> (raw)
do_sched_cfs_period_timer() will refill cfs_b runtime and call
distribute_cfs_runtime() to unthrottle cfs_rq, sometimes cfs_b->runtime
will allocate all quota to one cfs_rq incorrectly.
This will cause other cfs_rq can't get runtime and will be throttled.
We find that one throttled cfs_rq has non-negative
cfs_rq->runtime_remaining and cause an unexpetced cast from s64 to u64
in snippet: distribute_cfs_runtime() {
runtime = -cfs_rq->runtime_remaining + 1; }.
This cast will cause that runtime will be a large number and
cfs_b->runtime will be subtracted to be zero at last.
According to Ben Segall, the throttled cfs_rq can have
account_cfs_rq_runtime called on it because it is throttled before
idle_balance, and the idle_balance calls update_rq_clock to add time
that is accounted to the task.
This commit prevents cfs_rq to be assgined new runtime if it has been
throttled to avoid the above incorrect type cast.
Signed-off-by: Liangyan <liangyan.peng@linux.alibaba.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/sched/fair.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bc9cfeaac8bd..ac3ae694d850 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4470,6 +4470,8 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
if (likely(cfs_rq->runtime_remaining > 0))
return;
+ if (cfs_rq->throttled)
+ return;
/*
* if we're unable to extend our runtime we resched so that the active
* hierarchy can be throttled
@@ -4673,6 +4675,9 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
if (!cfs_rq_throttled(cfs_rq))
goto next;
+ /* By the above check, this should never be true */
+ WARN_ON(cfs_rq->runtime_remaining > 0);
+
runtime = -cfs_rq->runtime_remaining + 1;
if (runtime > remaining)
runtime = remaining;
--
2.14.4.44.g2045bb6
next reply other threads:[~2019-08-24 9:16 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-24 9:15 Liangyan [this message]
2019-08-26 9:25 ` [PATCH v2] sched/fair: don't assign runtime for throttled cfs_rq Peter Zijlstra
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