linux-kernel - Re: [PATCH v1] thermal: core: Move passive polling management to the core

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Message-ID: <5cf7d491-b0c1-4ffe-b66c-8c97331b7b76@arm.com>
Date: Mon, 29 Apr 2024 09:09:02 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>,
 Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v1] thermal: core: Move passive polling management to the
 core



On 4/25/24 15:11, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Passive polling is enabled by setting the 'passive' field in
> struct thermal_zone_device to a positive value so long as the
> 'passive_delay_jiffies' field is greater than zero.  It causes
> the thermal core to actively check the thermal zone temperature
> periodically which in theory should be done after crossing a
> passive trip point on the way up in order to allow governors to
> react more rapidly to temperature changes and adjust mitigation
> more precisely.
> 
> However, the 'passive' field in struct thermal_zone_device is currently
> managed by governors which is quite problematic.  First of all, only
> two governors, Step-Wise and Power Allocator, update that field at
> all, so the other governors do not benefit from passive polling,
> although in principle they should.  Moreover, if the zone governor is
> changed from, say, Step-Wise to Fair-Share after 'passive' has been
> incremented by the former, it is not going to be reset back to zero by
> the latter even if the zone temperature falls down below all passive
> trip points.
> 
> For this reason, make handle_thermal_trip() increment 'passive'
> to enable passive polling for the given thermal zone whenever a
> passive trip point is crossed on the way up and decrement it
> whenever a passive trip point is crossed on the way down.  Also
> remove the 'passive' field updates from governors and additionally
> clear it in thermal_zone_device_init() to prevent passive polling
> from being enabled after a system resume just beacuse it was enabled
> before suspending the system.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> This has been mentioned here:
> 
> https://lore.kernel.org/linux-pm/61560bc6-d453-4b0c-a4ea-b375d547b143@linaro.org/
> 
> and I need someone to double check if the Power Allocator governor does not
> need to be adjusted more for this change.

I'll do this today (and the rest of the patch as well).