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sched_ext: Replace SCX_TASK_BAL_KEEP with SCX_RQ_BAL_KEEP

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SCX_TASK_BAL_KEEP is used by balance_one() to tell pick_next_task_scx() to
keep running the current task. It's not really a task property. Replace it
with SCX_RQ_BAL_KEEP which resides in rq->scx.flags and is a better fit for
the usage. Also, the existing clearing rule is unnecessarily strict and
makes it difficult to use with core-sched. Just clear it on entry to
balance_one().

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2024-09-03 21:54:28 -10:00
parent 7c65ae81ea
commit 8b1451f2f7
3 changed files with 10 additions and 12 deletions
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1
include/linux/sched/ext.h
View File

@ -71,7 +71,6 @@ struct scx_dispatch_q {
/* scx_entity.flags */
enum scx_ent_flags {
SCX_TASK_QUEUED = 1 << 0, /* on ext runqueue */
SCX_TASK_BAL_KEEP = 1 << 1, /* balance decided to keep current */
SCX_TASK_RESET_RUNNABLE_AT = 1 << 2, /* runnable_at should be reset */
SCX_TASK_DEQD_FOR_SLEEP = 1 << 3, /* last dequeue was for SLEEP */

20
kernel/sched/ext.c
View File

@ -2508,6 +2508,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
lockdep_assert_rq_held(rq);
rq->scx.flags |= SCX_RQ_IN_BALANCE;
rq->scx.flags &= ~SCX_RQ_BAL_KEEP;
if (static_branch_unlikely(&scx_ops_cpu_preempt) &&
unlikely(rq->scx.cpu_released)) {
@ -2523,7 +2524,6 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
}
if (prev_on_scx) {
WARN_ON_ONCE(local && (prev->scx.flags & SCX_TASK_BAL_KEEP));
update_curr_scx(rq);
/*
@ -2538,13 +2538,13 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
*
* When balancing a remote CPU for core-sched, there won't be a
* following put_prev_task_scx() call and we don't own
* %SCX_TASK_BAL_KEEP. Instead, pick_task_scx() will test the
* same conditions later and pick @rq->curr accordingly.
* %SCX_RQ_BAL_KEEP. Instead, pick_task_scx() will test the same
* conditions later and pick @rq->curr accordingly.
*/
if ((prev->scx.flags & SCX_TASK_QUEUED) &&
prev->scx.slice && !scx_ops_bypassing()) {
if (local)
prev->scx.flags |= SCX_TASK_BAL_KEEP;
rq->scx.flags |= SCX_RQ_BAL_KEEP;
goto has_tasks;
}
}
@ -2604,7 +2604,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
if ((prev->scx.flags & SCX_TASK_QUEUED) &&
(!static_branch_unlikely(&scx_ops_enq_last) || scx_ops_bypassing())) {
if (local)
prev->scx.flags |= SCX_TASK_BAL_KEEP;
rq->scx.flags |= SCX_RQ_BAL_KEEP;
goto has_tasks;
}
rq->scx.flags &= ~SCX_RQ_IN_BALANCE;
@ -2726,8 +2726,6 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
SCX_CALL_OP_TASK(SCX_KF_REST, stopping, p, true);
if (p->scx.flags & SCX_TASK_QUEUED) {
p->scx.flags &= ~SCX_TASK_BAL_KEEP;
set_task_runnable(rq, p);
/*
@ -2772,8 +2770,8 @@ static struct task_struct *pick_next_task_scx(struct rq *rq,
* if necessary and keep running @prev. Otherwise, pop the first one
* from the local DSQ.
*/
if (prev->scx.flags & SCX_TASK_BAL_KEEP) {
prev->scx.flags &= ~SCX_TASK_BAL_KEEP;
if ((rq->scx.flags & SCX_RQ_BAL_KEEP) &&
!WARN_ON_ONCE(prev->sched_class != &ext_sched_class)) {
p = prev;
if (!p->scx.slice)
p->scx.slice = SCX_SLICE_DFL;
@ -2841,7 +2839,7 @@ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
*
* As put_prev_task_scx() hasn't been called on remote CPUs, we can't just look
* at the first task in the local dsq. @rq->curr has to be considered explicitly
* to mimic %SCX_TASK_BAL_KEEP.
* to mimic %SCX_RQ_BAL_KEEP.
*/
static struct task_struct *pick_task_scx(struct rq *rq)
{
@ -3872,7 +3870,7 @@ bool task_should_scx(struct task_struct *p)
*
* b. ops.dispatch() is ignored.
*
* c. balance_scx() does not set %SCX_TASK_BAL_KEEP on non-zero slice as slice
* c. balance_scx() does not set %SCX_RQ_BAL_KEEP on non-zero slice as slice
* can't be trusted. Whenever a tick triggers, the running task is rotated to
* the tail of the queue with core_sched_at touched.
*

1
kernel/sched/sched.h
View File

@ -737,6 +737,7 @@ enum scx_rq_flags {
*/
SCX_RQ_ONLINE = 1 << 0,
SCX_RQ_CAN_STOP_TICK = 1 << 1,
SCX_RQ_BAL_KEEP = 1 << 2, /* balance decided to keep current */
SCX_RQ_IN_WAKEUP = 1 << 16,
SCX_RQ_IN_BALANCE = 1 << 17,