linux-kernel - [PATCH] sched: fix exec_start/task

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Message-ID: <20140515225920.7179.13924.stgit@sword-of-the-dawn.mtv.corp.google.com>
Date:	Thu, 15 May 2014 15:59:20 -0700
From:	Ben Segall <bsegall@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] sched: fix exec_start/task_hot on migrated tasks

task_hot checks exec_start on any runnable task, but if it has been
migrated since the it last ran, then exec_start is a clock_task from
another cpu. If the old cpu's clock_task was sufficiently far ahead of
this cpu's then the task will not be considered for another migration
until it has run. Instead reset exec_start whenever a task is migrated,
since it is presumably no longer hot anyway.

Signed-off-by: Ben Segall <bsegall@...gle.com>
---
 kernel/sched/fair.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 28ccf50..9f8dfeb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4544,6 +4544,9 @@ migrate_task_rq_fair(struct task_struct *p, int next_cpu)
 		atomic_long_add(se->avg.load_avg_contrib,
 						&cfs_rq->removed_load);
 	}
+
+	/* We have migrated, no longer consider this task hot */
+	se.exec_start = 0;
 }
 #endif /* CONFIG_SMP */
 

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