sched/fair: Fix min_vruntime tracking
While going through enqueue/dequeue to review the movement of
set_curr_task() I noticed that the (2nd) update_min_vruntime() call in
dequeue_entity() is suspect.
It turns out, its actually wrong because it will consider
cfs_rq->curr, which could be the entry we just normalized. This mixes
different vruntime forms and leads to fail.
The purpose of the second update_min_vruntime() is to move
min_vruntime forward if the entity we just removed is the one that was
holding it back; _except_ for the DEQUEUE_SAVE case, because then we
know its a temporary removal and it will come back.
However, since we do put_prev_task() _after_ dequeue(), cfs_rq->curr
will still be set (and per the above, can be tranformed into a
different unit), so update_min_vruntime() should also consider
curr->on_rq. This also fixes another corner case where the enqueue
(which also does update_curr()->update_min_vruntime()) happens on the
rq->lock break in schedule(), between dequeue and put_prev_task.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Fixes: 1e87623178
("sched: Fix ->min_vruntime calculation in dequeue_entity()")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
parent
9148a3a10e
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@ -460,17 +460,23 @@ static inline int entity_before(struct sched_entity *a,
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static void update_min_vruntime(struct cfs_rq *cfs_rq)
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{
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struct sched_entity *curr = cfs_rq->curr;
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u64 vruntime = cfs_rq->min_vruntime;
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if (cfs_rq->curr)
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vruntime = cfs_rq->curr->vruntime;
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if (curr) {
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if (curr->on_rq)
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vruntime = curr->vruntime;
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else
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curr = NULL;
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}
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if (cfs_rq->rb_leftmost) {
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struct sched_entity *se = rb_entry(cfs_rq->rb_leftmost,
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struct sched_entity,
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run_node);
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if (!cfs_rq->curr)
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if (!curr)
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vruntime = se->vruntime;
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else
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vruntime = min_vruntime(vruntime, se->vruntime);
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@ -3478,9 +3484,10 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
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account_entity_dequeue(cfs_rq, se);
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/*
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* Normalize the entity after updating the min_vruntime because the
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* update can refer to the ->curr item and we need to reflect this
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* movement in our normalized position.
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* Normalize after update_curr(); which will also have moved
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* min_vruntime if @se is the one holding it back. But before doing
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* update_min_vruntime() again, which will discount @se's position and
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* can move min_vruntime forward still more.
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*/
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if (!(flags & DEQUEUE_SLEEP))
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se->vruntime -= cfs_rq->min_vruntime;
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@ -3488,8 +3495,16 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
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/* return excess runtime on last dequeue */
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return_cfs_rq_runtime(cfs_rq);
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update_min_vruntime(cfs_rq);
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update_cfs_shares(cfs_rq);
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/*
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* Now advance min_vruntime if @se was the entity holding it back,
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* except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case we'll be
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* put back on, and if we advance min_vruntime, we'll be placed back
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* further than we started -- ie. we'll be penalized.
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*/
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if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
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update_min_vruntime(cfs_rq);
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}
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/*
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