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Subject[PATCH] sched: fix exec_start/task_hot on migrated tasks
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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@google.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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