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sched_ext: Drop the locks periodically while walking a user DSQ for re-enqueue

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reenq_user() drops dsq->lock around each re-enqueue and its rq lock every
SCX_TASK_ITER_BATCH re-enqueues. A walk filtered by SCX_REENQ_MARKED skips
unmarked tasks without dropping either, so a long run of unmarked tasks is
walked in one hold of both locks.

Count the visited tasks instead of the re-enqueued ones and drop both locks
every SCX_TASK_ITER_BATCH visits. An unfiltered walk drops the locks as
often as before.

Suggested-by: Andrea Righi <arighi@nvidia.com>
Link: https://lore.kernel.org/all/atP-LIKpxPhR-Nuc@gpd4/
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-10-17 13:56:04 -10:00
parent cce3618e2d
commit 1f5dde349a
1 changed files with 16 additions and 8 deletions
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24
kernel/sched/ext/ext.c
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@ -5111,7 +5111,7 @@ static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flag
struct scx_sched *sch = dsq->sched;
struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, dsq, 0);
struct task_struct *p;
s32 nr_enqueued = 0;
s32 nr_visited = 0;
lockdep_assert_rq_held(rq);
@ -5121,6 +5121,21 @@ static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flag
struct rq *task_rq;
u32 reason;
/*
* Count skipped tasks too so that a long walk doesn't hold the
* locks throughout. The cursor keeps the position.
*/
if (!(++nr_visited % SCX_TASK_ITER_BATCH)) {
raw_spin_unlock(&dsq->lock);
if (locked_rq) {
scx_rq_lock_drop(locked_rq);
raw_spin_rq_unlock(locked_rq);
locked_rq = NULL;
}
cpu_relax();
raw_spin_lock(&dsq->lock);
}
p = nldsq_cursor_next_task(&cursor, dsq);
if (!p)
break;
@ -5157,13 +5172,6 @@ static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flag
scx_do_enqueue_task(task_rq, p, SCX_ENQ_REENQ, -1);
if (!(++nr_enqueued % SCX_TASK_ITER_BATCH)) {
scx_rq_lock_drop(locked_rq);
raw_spin_rq_unlock(locked_rq);
locked_rq = NULL;
cpu_relax();
}
raw_spin_lock(&dsq->lock);
}