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

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Message-ID: <Z3wmoFPes_Qb-hTg@slm.duckdns.org>
Date: Mon, 6 Jan 2025 08:53:20 -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 Sat, Jan 04, 2025 at 08:06:26AM +0100, Andrea Righi wrote:
...
> The issue is that we call ops.update_idle() when a CPU enters or exits
> SCHED_IDLE, whereas it should ideally be called when the CPU transitions
> in/out of the idle state. So perhaps a kick from idle should trigger
> ops.update_idle(cpu, false)? Still, I'm not sure if that would provide any
> benefit... after all, do you see any practical scenarios where having
> unbalanced transitions could be a problem?

If possible, we should keep the calls balanced even if that means a bit of
complications on the core side as these things can become subtle bugs from
BPF scheduler side. And, yeah, I think kicking transitioning the CPU out of
idle makes sense to me.

Thanks.

-- 
tejun