linux-kernel - Re: [PATCH v1 1/4] cpuidle: teo: Add polling flag check to early return path

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Message-ID: <00fffcc11f41ffd069c499010e89244d4ccb6cec.camel@gmail.com>
Date: Thu, 23 Jan 2025 18:54:33 +0200
From: Artem Bityutskiy <dedekind1@...il.com>
To: Christian Loehle <christian.loehle@....com>, "Rafael J. Wysocki"
 <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, Aboorva Devarajan
 <aboorvad@...ux.ibm.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Daniel Lezcano
	 <daniel.lezcano@...aro.org>
Subject: Re: [PATCH v1 1/4] cpuidle: teo: Add polling flag check to early
 return path

On Fri, 2025-01-10 at 13:16 +0000, Christian Loehle wrote:
> This would then enable intercept-detection only for <50% of the time,
> another option is to not allow intercepts selecting a polling state, but
> there were recent complaints about this exact behavior from Aboorva (+TO).
> They don't have a low-latency non-polling state.

What folks think about the following idea.

Idle governor algorithm essentially predicts the sleep time (step 1), based on
that, the idle state gets selected (step 2).

What if we add a sleep time factor and expose it via sysfs. The predicted sleep
time would be multiplied by the factor (between steps 1 and 2).

Default factor value is 1 (or 100%). If users want teo be more hesitant
selecting deeper idle states, they can set it to 0.5 (or 50%) or some other
value < 1. I users want teo to be more enthusiastic about selecting deeper idle
states, they set the factor to a value > 1.

We could expose it via sysfs and allow changing in some reasonable range.

The idea is to let users adjust the level of idle governor (teo in this case)
enthusiasm regarding deep C-state.

Thanks,
Artem.