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Subject[PATCH 1/2] sched/fair: Don't rely on ->exec_start for migration
Date
From: Peter Zijlstra <peterz@infradead.org>

From: Peter Zijlstra (Intel) <peterz@infradead.org>

Currently migrate_task_rq_fair() (ab)uses se->exec_start to make
task_hot() fail. In order to preserve ->exec_start, add a ->migrated
flag to sched_entity.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
include/linux/sched.h | 1 +
kernel/sched/fair.c | 6 +++++-
2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 75ba8aa60248..0edf16b4d40a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -541,6 +541,7 @@ struct sched_entity {
struct rb_node run_node;
struct list_head group_node;
unsigned int on_rq;
+ unsigned int migrated;

u64 exec_start;
u64 sum_exec_runtime;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5146163bfabb..2498e97804fd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1004,6 +1004,7 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
/*
* We are starting a new run period:
*/
+ se->migrated = 0;
se->exec_start = rq_clock_task(rq_of(cfs_rq));
}

@@ -6979,7 +6980,7 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu)
p->se.avg.last_update_time = 0;

/* We have migrated, no longer consider this task hot */
- p->se.exec_start = 0;
+ p->se.migrated = 1;

update_scan_period(p, new_cpu);
}
@@ -7665,6 +7666,9 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
if (sysctl_sched_migration_cost == 0)
return 0;

+ if (p->se.migrated)
+ return 0;
+
delta = rq_clock_task(env->src_rq) - p->se.exec_start;

return delta < (s64)sysctl_sched_migration_cost;
--
2.32.0
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