From: Odin Ugedal <odin@uged.al>
To: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
Odin Ugedal <odin@uged.al>
Subject: [PATCH 1/3] sched/fair: Add tg_load_contrib cfs_rq decay checking
Date: Tue, 18 May 2021 14:52:00 +0200 [thread overview]
Message-ID: <20210518125202.78658-2-odin@uged.al> (raw)
In-Reply-To: <20210518125202.78658-1-odin@uged.al>
Make sure cfs_rq does not contribute to task group load avg when
checking if it is decayed. Due to how the pelt tracking works,
the divider can result in a situation where:
cfs_rq->avg.load_sum = 0
cfs_rq->avg.load_avg = 4
cfs_rq->avg.tg_load_avg_contrib = 4
If pelt tracking in this case does not cross a period, there is no
"change" in load_sum, and therefore load_avg is not recalculated, and
keeps its value.
If this cfs_rq is then removed from the leaf list, it results in a
situation where the load is never removed from the tg. If that happen,
the fiarness is permanently skewed.
Fixes: 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path")
Signed-off-by: Odin Ugedal <odin@uged.al>
---
kernel/sched/fair.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3248e24a90b0..ceda53c2a87a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8004,6 +8004,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
if (cfs_rq->avg.runnable_sum)
return false;
+ if (cfs_rq->tg_load_avg_contrib)
+ return false;
+
return true;
}
--
2.31.1
next prev parent reply other threads:[~2021-05-18 12:55 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-18 12:51 [PATCH 0/3] sched/fair: Fix load decay issues related to throttling Odin Ugedal
2021-05-18 12:52 ` Odin Ugedal [this message]
2021-05-25 9:58 ` [PATCH 1/3] sched/fair: Add tg_load_contrib cfs_rq decay checking Vincent Guittot
2021-05-25 10:33 ` Odin Ugedal
2021-05-25 14:30 ` Vincent Guittot
2021-05-26 10:50 ` Vincent Guittot
2021-05-27 7:50 ` Odin Ugedal
2021-05-27 9:35 ` Vincent Guittot
2021-05-27 9:45 ` Odin Ugedal
2021-05-27 10:49 ` Vincent Guittot
2021-05-27 11:04 ` Odin Ugedal
2021-05-27 12:37 ` Vincent Guittot
2021-05-27 12:37 ` Odin Ugedal
2021-05-27 12:39 ` Odin Ugedal
2021-05-27 12:49 ` Vincent Guittot
2021-05-18 12:52 ` [PATCH 2/3] sched/fair: Correctly insert cfs_rq's to list on unthrottle Odin Ugedal
2021-05-28 14:24 ` Vincent Guittot
2021-05-28 15:06 ` Odin Ugedal
2021-05-28 15:27 ` Vincent Guittot
2021-05-29 9:33 ` Odin Ugedal
2021-05-31 12:14 ` Vincent Guittot
2021-05-18 12:52 ` [PATCH 3/3] sched/fair: Fix ascii art by relpacing tabs Odin Ugedal
2021-05-27 13:27 ` Vincent Guittot
2021-06-01 14:04 ` [tip: sched/core] " tip-bot2 for Odin Ugedal
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