This is a note to let you know that I've just added the patch titled
sched/fair: Sanitize vruntime of entity being migrated
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-fair-sanitize-vruntime-of-entity-being-migrated.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a53ce18cacb477dd0513c607f187d16f0fa96f71 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date: Fri, 17 Mar 2023 17:08:10 +0100
Subject: sched/fair: Sanitize vruntime of entity being migrated
From: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
commit a53ce18cacb477dd0513c607f187d16f0fa96f71 upstream.
Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed")
fixes an overflowing bug, but ignore a case that se->exec_start is reset
after a migration.
For fixing this case, we delay the reset of se->exec_start after
placing the entity which se->exec_start to detect long sleeping task.
In order to take into account a possible divergence between the clock_task
of 2 rqs, we increase the threshold to around 104 days.
Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed")
Originally-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230317160810.107988-1-vincent.guittot@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/core.c | 3 ++
kernel/sched/fair.c | 53 ++++++++++++++++++++++++++++++++++++++++++----------
2 files changed, 46 insertions(+), 10 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1411,6 +1411,9 @@ static inline void dequeue_task(struct r
void activate_task(struct rq *rq, struct task_struct *p, int flags)
{
+ if (task_on_rq_migrating(p))
+ flags |= ENQUEUE_MIGRATED;
+
if (task_contributes_to_load(p))
rq->nr_uninterruptible--;
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3877,11 +3877,33 @@ static void check_spread(struct cfs_rq *
#endif
}
+static inline bool entity_is_long_sleeper(struct sched_entity *se)
+{
+ struct cfs_rq *cfs_rq;
+ u64 sleep_time;
+
+ if (se->exec_start == 0)
+ return false;
+
+ cfs_rq = cfs_rq_of(se);
+
+ sleep_time = rq_clock_task(rq_of(cfs_rq));
+
+ /* Happen while migrating because of clock task divergence */
+ if (sleep_time <= se->exec_start)
+ return false;
+
+ sleep_time -= se->exec_start;
+ if (sleep_time > ((1ULL << 63) / scale_load_down(NICE_0_LOAD)))
+ return true;
+
+ return false;
+}
+
static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
u64 vruntime = cfs_rq->min_vruntime;
- u64 sleep_time;
/*
* The 'current' period is already promised to the current tasks,
@@ -3908,13 +3930,24 @@ place_entity(struct cfs_rq *cfs_rq, stru
/*
* Pull vruntime of the entity being placed to the base level of
- * cfs_rq, to prevent boosting it if placed backwards. If the entity
- * slept for a long time, don't even try to compare its vruntime with
- * the base as it may be too far off and the comparison may get
- * inversed due to s64 overflow.
+ * cfs_rq, to prevent boosting it if placed backwards.
+ * However, min_vruntime can advance much faster than real time, with
+ * the extreme being when an entity with the minimal weight always runs
+ * on the cfs_rq. If the waking entity slept for a long time, its
+ * vruntime difference from min_vruntime may overflow s64 and their
+ * comparison may get inversed, so ignore the entity's original
+ * vruntime in that case.
+ * The maximal vruntime speedup is given by the ratio of normal to
+ * minimal weight: scale_load_down(NICE_0_LOAD) / MIN_SHARES.
+ * When placing a migrated waking entity, its exec_start has been set
+ * from a different rq. In order to take into account a possible
+ * divergence between new and prev rq's clocks task because of irq and
+ * stolen time, we take an additional margin.
+ * So, cutting off on the sleep time of
+ * 2^63 / scale_load_down(NICE_0_LOAD) ~ 104 days
+ * should be safe.
*/
- sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start;
- if ((s64)sleep_time > 60LL * NSEC_PER_SEC)
+ if (entity_is_long_sleeper(se))
se->vruntime = vruntime;
else
se->vruntime = max_vruntime(se->vruntime, vruntime);
@@ -4013,6 +4046,9 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
if (flags & ENQUEUE_WAKEUP)
place_entity(cfs_rq, se, 0);
+ /* Entity has migrated, no longer consider this task hot */
+ if (flags & ENQUEUE_MIGRATED)
+ se->exec_start = 0;
check_schedstat_required();
update_stats_enqueue(cfs_rq, se, flags);
@@ -6638,9 +6674,6 @@ static void migrate_task_rq_fair(struct
/* Tell new CPU we are migrated */
p->se.avg.last_update_time = 0;
- /* We have migrated, no longer consider this task hot */
- p->se.exec_start = 0;
-
update_scan_period(p, new_cpu);
}
Patches currently in stable-queue which might be from vincent.guittot@xxxxxxxxxx are
queue-5.4/sched-fair-sanitize-vruntime-of-entity-being-migrated.patch
