Re: [RFC PATCH 06/16] sched/core: Queue blocked donor onto sleeping owner for chain-wakeup

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Andrea,

On 8/26/2026 9:50 PM, Andrea Righi wrote:
>> +static void proxy_enqueue_on_owner(struct rq *rq, struct task_struct *owner,
>> +				   struct task_struct *p)
>> +{
>> +	lockdep_assert_rq_held(rq);
>> +	lockdep_assert_held(&owner->blocked_lock);
>> +
>> +	WARN_ON(!p->on_rq);
>> +	WARN_ON(p->sleeping_owner);
>> +
>> +	WRITE_ONCE(p->sleeping_owner, owner);
>> +	list_add(&p->blocked_node, &owner->blocked_head);
>> +	proxy_resched_idle(rq);
>> +
>> +	/*
>> +	 * Order against __activate_blocked_task_slowpath() checking
>> +	 * owner->blocked_list after setting owner->on_rq.
> 
> This should be owner->blocked_head not owner->blocked_list, right?

Correct! My bad. Also the slow-path is proxy_activate_blocked_task()
that gets introduced in Patch 14. I missed renaming it here.

And ack on other comments too above.

> 
>> +	 */
>> +	smp_mb();
>> +
>> +	if (READ_ONCE(owner->on_rq)) {
>> +		/*
>> +		 * owner has woken up and may miss activating us.
>> +		 * Remove ourself from "owner->blocked_head" and try
>> +		 * find_proxy_task() again considering the owner's
>> +		 * new state.
>> +		 */
>> +		__proxy_dequeue_from_owner(p);
>> +		return;
>> +	}
>> +
>> +	/*
>> +	 * Owner is fully blocked. __activate_blocked_task_slowpath()
>> +	 * will see us on the list during wakeup and DTRT.
>> +	 */
>> +	block_task(rq, p, READ_ONCE(p->__state));
>> +}

-- 
Thanks and Regards,
Prateek