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sched_ext: Remove scx_ops_cpu_preempt static_key

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scx_ops_cpu_preempt is used to encode whether ops.cpu_acquire/release() are
implemented into a static_key. These tests aren't hot enough for static_key
usage to make any meaningful difference and are made to use a static_key
mostly because there was no reason not to. However, global static_keys can't
work with the planned hierarchical multiple scheduler support. Remove the
static_key and instead use an internal ops flag SCX_OPS_HAS_CPU_PREEMPT to
record and test whether ops.cpu_acquire/release() are implemented.

In repeated hackbench runs before and after static_keys removal on an AMD
Ryzen 3900X, I couldn't tell any measurable performance difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2025-04-09 09:06:00 -10:00
parent cc39454c34
commit 54d2e717bc
1 changed files with 8 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

13
kernel/sched/ext.c
View file

@ -173,6 +173,11 @@ enum scx_ops_flags {
SCX_OPS_SWITCH_PARTIAL |
SCX_OPS_BUILTIN_IDLE_PER_NODE |
SCX_OPS_HAS_CGROUP_WEIGHT,
/* high 8 bits are internal, don't include in SCX_OPS_ALL_FLAGS */
__SCX_OPS_INTERNAL_MASK = 0xffLLU << 56,
SCX_OPS_HAS_CPU_PREEMPT = 1LLU << 56,
};
/* argument container for ops.init_task() */
@ -924,7 +929,6 @@ static struct sched_ext_ops scx_ops;
static bool scx_warned_zero_slice;
DEFINE_STATIC_KEY_FALSE(scx_ops_allow_queued_wakeup);
static DEFINE_STATIC_KEY_FALSE(scx_ops_cpu_preempt);
static struct static_key_false scx_has_op[SCX_OPI_END] =
{ [0 ... SCX_OPI_END-1] = STATIC_KEY_FALSE_INIT };
@ -2931,7 +2935,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
rq->scx.flags |= SCX_RQ_IN_BALANCE;
rq->scx.flags &= ~(SCX_RQ_BAL_PENDING | SCX_RQ_BAL_KEEP);
if (static_branch_unlikely(&scx_ops_cpu_preempt) &&
if ((scx_ops.flags & SCX_OPS_HAS_CPU_PREEMPT) &&
unlikely(rq->scx.cpu_released)) {
/*
* If the previous sched_class for the current CPU was not SCX,
@ -3160,7 +3164,7 @@ static void switch_class(struct rq *rq, struct task_struct *next)
*/
smp_store_release(&rq->scx.pnt_seq, rq->scx.pnt_seq + 1);
#endif
if (!static_branch_unlikely(&scx_ops_cpu_preempt))
if (!(scx_ops.flags & SCX_OPS_HAS_CPU_PREEMPT))
return;
/*
@ -4725,7 +4729,6 @@ static void scx_disable_workfn(struct kthread_work *work)
for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++)
static_branch_disable(&scx_has_op[i]);
static_branch_disable(&scx_ops_allow_queued_wakeup);
static_branch_disable(&scx_ops_cpu_preempt);
scx_idle_disable();
synchronize_rcu();
@ -5367,7 +5370,7 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
if (ops->flags & SCX_OPS_ALLOW_QUEUED_WAKEUP)
static_branch_enable(&scx_ops_allow_queued_wakeup);
if (scx_ops.cpu_acquire || scx_ops.cpu_release)
static_branch_enable(&scx_ops_cpu_preempt);
scx_ops.flags |= SCX_OPS_HAS_CPU_PREEMPT;
/*
* Lock out forks, cgroup on/offlining and moves before opening the