From: Qais Yousef <qais.yousef@arm.com>
To: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Pavan Kondeti <pkondeti@codeaurora.org>
Cc: Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel@vger.kernel.org, Qais Yousef <qais.yousef@arm.com>
Subject: [PATCH v3 2/6] sched/rt: Re-instate old behavior in select_task_rq_rt
Date: Mon, 2 Mar 2020 13:27:17 +0000 [thread overview]
Message-ID: <20200302132721.8353-3-qais.yousef@arm.com> (raw)
In-Reply-To: <20200302132721.8353-1-qais.yousef@arm.com>
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@codeaurora.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@arm.com>
---
Notes:
Changes since v2:
* Check that target != -1 (thanks Dietmar)
kernel/sched/rt.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4043abe45459..0afc70c9b68b 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 && target != -1 && !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
next prev parent reply other threads:[~2020-03-02 13:27 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-02 13:27 [PATCH v3 0/6] RT Capacity Awareness Fixes & Improvements Qais Yousef
2020-03-02 13:27 ` [PATCH v3 1/6] sched/rt: cpupri_find: Implement fallback mechanism for !fit case Qais Yousef
[not found] ` <20200304143200.GA13200@geo.homenetwork>
2020-03-04 15:18 ` Qais Yousef
2020-03-04 16:27 ` Steven Rostedt
2020-03-04 17:39 ` Qais Yousef
2020-03-04 18:54 ` Steven Rostedt
2020-03-04 20:01 ` Qais Yousef
2020-03-05 12:43 ` Qais Yousef
2020-03-10 14:22 ` Qais Yousef
2020-03-11 13:51 ` Steven Rostedt
2020-03-20 12:58 ` [tip: sched/core] sched/rt: cpupri_find: Trigger a full search as fallback tip-bot2 for Qais Yousef
2020-03-06 14:42 ` [tip: sched/core] sched/rt: cpupri_find: Implement fallback mechanism for !fit case tip-bot2 for Qais Yousef
2020-03-02 13:27 ` Qais Yousef [this message]
2020-03-06 14:42 ` [tip: sched/core] sched/rt: Re-instate old behavior in select_task_rq_rt() tip-bot2 for Qais Yousef
2020-03-02 13:27 ` [PATCH v3 3/6] sched/rt: Optimize cpupri_find on non-heterogenous systems Qais Yousef
2020-03-06 14:42 ` [tip: sched/core] sched/rt: Optimize cpupri_find() " tip-bot2 for Qais Yousef
2020-03-02 13:27 ` [PATCH v3 4/6] sched/rt: Allow pulling unfitting task Qais Yousef
[not found] ` <20200304145219.GA14173@geo.homenetwork>
2020-03-04 15:28 ` Qais Yousef
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Qais Yousef
2020-03-02 13:27 ` [PATCH v3 5/6] sched/rt: Remove unnecessary push for unfit tasks Qais Yousef
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Qais Yousef
2020-03-02 13:27 ` [PATCH v3 6/6] sched/rt: Fix pushing unfit tasks to a better CPU Qais Yousef
2020-03-06 17:51 ` Qais Yousef
2020-03-11 10:53 ` Pavan Kondeti
2020-03-11 14:11 ` Qais Yousef
2020-03-11 14:00 ` Steven Rostedt
2020-03-11 14:23 ` Qais Yousef
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