[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200223184001.14248-3-qais.yousef@arm.com>
Date: Sun, 23 Feb 2020 18:39:57 +0000
From: Qais Yousef <qais.yousef@....com>
To: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Pavan Kondeti <pkondeti@...eaurora.org>
Cc: Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
linux-kernel@...r.kernel.org, Qais Yousef <qais.yousef@....com>
Subject: [PATCH v2 2/6] sched/rt: Re-instate old behavior in select_task_rq_rt
When RT Capacity Aware support was added, the logic in select_task_rq_rt
was modified to force a search for a fitting CPU if the task currently
doesn't run on one.
But if the search failed, and the search was only triggered to fulfill
the fitness request; we could end up selecting a new CPU unnecessarily.
Fix this and re-instate the original behavior by ensuring we bail out
in that case.
This behavior change only affected asymmetric systems that are using
util_clamp to implement capacity aware. None asymmetric systems weren't
affected.
Reported-by: Pavan Kondeti <pkondeti@...eaurora.org>
Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware")
LINK: https://lore.kernel.org/lkml/20200218041620.GD28029@codeaurora.org/
Signed-off-by: Qais Yousef <qais.yousef@....com>
---
kernel/sched/rt.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4043abe45459..2c3fae637cef 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1474,6 +1474,13 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
if (test || !rt_task_fits_capacity(p, cpu)) {
int target = find_lowest_rq(p);
+ /*
+ * Bail out if we were forcing a migration to find a better
+ * fitting CPU but our search failed.
+ */
+ if (!test && !rt_task_fits_capacity(p, target))
+ goto out_unlock;
+
/*
* Don't bother moving it if the destination CPU is
* not running a lower priority task.
@@ -1482,6 +1489,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
p->prio < cpu_rq(target)->rt.highest_prio.curr)
cpu = target;
}
+
+out_unlock:
rcu_read_unlock();
out:
--
2.17.1
Powered by blists - more mailing lists