linux-kernel - Re: [PATCH] sched_ext: Refresh idle state when kicking CPUs

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Message-ID: <Z3cUIkOkfZ3n-XTz@slm.duckdns.org>
Date: Thu, 2 Jan 2025 12:33:06 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched_ext: Refresh idle state when kicking CPUs

Hello,

On Wed, Jan 01, 2025 at 07:24:49PM +0100, Andrea Righi wrote:
...
> @@ -6104,6 +6117,7 @@ static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *pseqs)
>  			should_wait = true;
>  		}
>  
> +		refresh_idle_state_on_kick(rq);
>  		resched_curr(rq);

I'm not sure this is quite correct. e.g. This can cause multiple
back-to-back busy->busy transitions and can incorrectly assert idle when the
CPU ends up running non-idle tasks afterwards.

When the put_prev/set_next paths were reorganized, we lost the signal on the
CPU re-entering idle from idle. However, that signal is still available if
we hook into idle_class->pick_task(), right? So, if we move
update_idle(true) call there and make sure that we don't generate an event
on busy->busy transitions, we should be able to restore the previous
behavior?

Thanks.

-- 
tejun