[PATCH AUTOSEL 6.12 17/20] sched_ext: keep running prev when prev->scx.slice != 0

Sasha Levin
2025-01-13T18:35:05Z

From: Henry Huang <henry.hj@antgroup.com>

[ Upstream commit 30dd3b13f9de612ef7328ccffcf1a07d0d40ab51 ]

When %SCX_OPS_ENQ_LAST is set and prev->scx.slice != 0,
@prev will be dispacthed into the local DSQ in put_prev_task_scx().
However, pick_task_scx() is executed before put_prev_task_scx(),
so it will not pick @prev.
Set %SCX_RQ_BAL_KEEP in balance_one() to ensure that pick_task_scx()
can pick @prev.

Signed-off-by: Henry Huang <henry.hj@antgroup.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sched/ext.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 40f915f893e2..7e217761854b 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2630,6 +2630,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
{
struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
bool prev_on_scx = prev->sched_class == &ext_sched_class;
+ bool prev_on_rq = prev->scx.flags & SCX_TASK_QUEUED;
int nr_loops = SCX_DSP_MAX_LOOPS;

lockdep_assert_rq_held(rq);
@@ -2662,8 +2663,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
* See scx_ops_disable_workfn() for the explanation on the
* bypassing test.
*/
- if ((prev->scx.flags & SCX_TASK_QUEUED) &&
- prev->scx.slice && !scx_rq_bypassing(rq)) {
+ if (prev_on_rq && prev->scx.slice && !scx_rq_bypassing(rq)) {
rq->scx.flags |= SCX_RQ_BAL_KEEP;
goto has_tasks;
}
@@ -2696,6 +2696,10 @@ static int balance_one(struct rq *rq, struct task_struct *prev)

flush_dispatch_buf(rq);

+ if (prev_on_rq && prev->scx.slice) {
+ rq->scx.flags |= SCX_RQ_BAL_KEEP;
+ goto has_tasks;
+ }
if (rq->scx.local_dsq.nr)
goto has_tasks;
if (consume_global_dsq(rq))
@@ -2721,8 +2725,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
* Didn't find another task to run. Keep running @prev unless
* %SCX_OPS_ENQ_LAST is in effect.
*/
- if ((prev->scx.flags & SCX_TASK_QUEUED) &&
- (!static_branch_unlikely(&scx_ops_enq_last) ||
+ if (prev_on_rq && (!static_branch_unlikely(&scx_ops_enq_last) ||
scx_rq_bypassing(rq))) {
rq->scx.flags |= SCX_RQ_BAL_KEEP;
goto has_tasks;
--
2.39.5