Commit 62607d03 authored Aug 30, 2024 by Tejun Heo

sched_ext: Use sched_clock_cpu() instead of rq_clock_task() in touch_core_sched()

Since 3cf78c5d ("sched_ext: Unpin and repin rq lock from
balance_scx()"), sched_ext's balance path terminates rq_pin in the outermost
function. This is simpler and in line with what other balance functions are
doing but it loses control over rq->clock_update_flags which makes
assert_clock_udpated() trigger if other CPUs pins the rq lock.

The only place this matters is touch_core_sched() which uses the timestamp
to order tasks from sibling rq's. Switch to sched_clock_cpu(). Later, it may
be better to use per-core dispatch sequence number.

v2: Use sched_clock_cpu() instead of ktime_get_ns() per David.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 3cf78c5d ("sched_ext: Unpin and repin rq lock from balance_scx()")
Acked-by: David Vernet <void@manifault.com>
Cc: Peter Zijlstra <peterz@infradead.org>

parent 0366017e

kernel/sched/ext.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -1453,13 +1453,18 @@ static void schedule_deferred(struct rq *rq)
		*/
		static void touch_core_sched(struct rq rq, struct task_struct p)
		{
		lockdep_assert_rq_held(rq);

		#ifdef CONFIG_SCHED_CORE
		/*
		* It's okay to update the timestamp spuriously. Use
		* sched_core_disabled() which is cheaper than enabled().
		*
		* As this is used to determine ordering between tasks of sibling CPUs,
		* it may be better to use per-core dispatch sequence instead.
		*/
		if (!sched_core_disabled())
		p->scx.core_sched_at = rq_clock_task(rq);
		p->scx.core_sched_at = sched_clock_cpu(cpu_of(rq));
		#endif
		}

		@@ -1476,7 +1481,6 @@ static void touch_core_sched(struct rq rq, struct task_struct p)
		static void touch_core_sched_dispatch(struct rq rq, struct task_struct p)
		{
		lockdep_assert_rq_held(rq);
		assert_clock_updated(rq);

		#ifdef CONFIG_SCHED_CORE
		if (SCX_HAS_OP(core_sched_before))