kernel/sched/fair.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 55294004b122c997591d9de8446f5a4c60402805
Gitweb: https://git.kernel.org/tip/55294004b122c997591d9de8446f5a4c60402805
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 28 Jan 2025 15:39:49 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Sat, 08 Feb 2025 15:43:12 +01:00
sched/fair: Adhere to place_entity() constraints
Mike reports that commit 6d71a9c61604 ("sched/fair: Fix EEVDF entity
placement bug causing scheduling lag") relies on commit 4423af84b297
("sched/fair: optimize the PLACE_LAG when se->vlag is zero") to not
trip a WARN in place_entity().
What happens is that the lag of the very last entity is 0 per
definition -- the average of one element matches the value of that
element. Therefore place_entity() will match the condition skipping
the lag adjustment:
if (sched_feat(PLACE_LAG) && cfs_rq->nr_queued && se->vlag) {
Without the 'se->vlag' condition -- it will attempt to adjust the zero
lag even though we're inserting into an empty tree.
Notably, we should have failed the 'cfs_rq->nr_queued' condition, but
don't because they didn't get updated.
Additionally, move update_load_add() after placement() as is
consistent with other place_entity() users -- this change is
non-functional, place_entity() does not use cfs_rq->load.
Fixes: 6d71a9c61604 ("sched/fair: Fix EEVDF entity placement bug causing scheduling lag")
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20250128143949.GD7145@noisy.programming.kicks-ass.net
---
kernel/sched/fair.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f4e4d3e..d0b10e1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3782,6 +3782,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
update_entity_lag(cfs_rq, se);
se->deadline -= se->vruntime;
se->rel_deadline = 1;
+ cfs_rq->nr_queued--;
if (!curr)
__dequeue_entity(cfs_rq, se);
update_load_sub(&cfs_rq->load, se->load.weight);
@@ -3808,10 +3809,11 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
enqueue_load_avg(cfs_rq, se);
if (se->on_rq) {
- update_load_add(&cfs_rq->load, se->load.weight);
place_entity(cfs_rq, se, 0);
+ update_load_add(&cfs_rq->load, se->load.weight);
if (!curr)
__enqueue_entity(cfs_rq, se);
+ cfs_rq->nr_queued++;
/*
* The entity's vruntime has been adjusted, so let's check> The following commit has been merged into the sched/urgent branch of tip: > > Commit-ID: 55294004b122c997591d9de8446f5a4c60402805 > Gitweb: https://git.kernel.org/tip/55294004b122c997591d9de8446f5a4c60402805 > Author: Peter Zijlstra <peterz@infradead.org> > AuthorDate: Tue, 28 Jan 2025 15:39:49 +01:00 > Committer: Peter Zijlstra <peterz@infradead.org> > CommitterDate: Sat, 08 Feb 2025 15:43:12 +01:00 Was this merged to sched/urgent or any other branches/RCs? Given gitweb link sends me to "Bad commit reference". I don't see this commit in sched/urgent: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=sched%2Furgent
On Fri, 2025-05-23 at 16:01 +0000, Mushahid Hussain wrote: > > The following commit has been merged into the sched/urgent branch of tip: > > > > Commit-ID: 55294004b122c997591d9de8446f5a4c60402805 > > Gitweb: https://git.kernel.org/tip/55294004b122c997591d9de8446f5a4c60402805 > > Author: Peter Zijlstra <peterz@infradead.org> > > AuthorDate: Tue, 28 Jan 2025 15:39:49 +01:00 > > Committer: Peter Zijlstra <peterz@infradead.org> > > CommitterDate: Sat, 08 Feb 2025 15:43:12 +01:00 > > Was this merged to sched/urgent or any other branches/RCs? Given gitweb link > sends me to "Bad commit reference". I don't see this commit in sched/urgent: > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=sched%2Furgent I think something weird has just happened to the tip tree. All the tip/x86/* branches also seem to have been reset to Linux 6.15-rc6.
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