Commit 54d2e717 authored by Tejun Heo's avatar Tejun Heo
Browse files

sched_ext: Remove scx_ops_cpu_preempt static_key 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarChangwoo Min <changwoo@igalia.com>
Acked-by: default avatarAndrea Righi <arighi@nvidia.com>
parent cc39454c

kernel/sched/ext.c

+8 −5
Original line number Diff line number Diff line
@@ -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