linux-kernel - RE: [PATCH v1] cpuidle: governors: menu: Always check timers with tick stopped

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Message-ID: <004801dc9015$b9715ec0$2c541c40$@telus.net>
Date: Tue, 27 Jan 2026 21:19:48 -0800
From: "Doug Smythies" <dsmythies@...us.net>
To: "'Rafael J. Wysocki'" <rafael@...nel.org>,
	"'Christian Loehle'" <christian.loehle@....com>
Cc: "'LKML'" <linux-kernel@...r.kernel.org>,
	"'Linux PM'" <linux-pm@...r.kernel.org>,
	"Doug Smythies" <dsmythies@...us.net>
Subject: RE: [PATCH v1] cpuidle: governors: menu: Always check timers with tick stopped

On 2026.01.20 07:26 Rafael J. Wysocki wrote:
>From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> After commit 5484e31bbbff ("cpuidle: menu: Skip tick_nohz_get_sleep_length()
> call in some cases"), if the return value of get_typical_interval()
> multiplied by NSEC_PER_USEC is not greater than RESIDENCY_THRESHOLD_NS,
> the menu governor will skip computing the time till the closest timer.
> If that happens when the tick has been stopped already, the selected
> idle state may be too deep due to the subsequent check comparing
> predicted_ns with TICK_NSEC and causing its value to be replaced with
> the expected time till the closest timer, which is KTIME_MAX in that
> case.  That will cause the deepest enabled idle state to be selected,
> but the time till the closest timer very well may be shorter than the
> target residency of that state, in which case a shallower state should
> be used.
>
> Address this by making menu_select() always compute the time till the
> closest timer when the tick has been stopped.
>
> Also move the predicted_ns check mentioned above into the branch in
> which the time till the closest timer is determined because it only
> needs to be done in that case.
>
> Fixes: 5484e31bbbff ("cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

... snip ...

I have been testing with this patch, and have not observed any difference
in test results and energy use with and without this patch.
A couple of graphs are attached.
I did this work on top of the teo work, so those results are on the graphs also.

Legend:
rc5 = kernel 6.19-rc5
rjw = kernel 6.19-rc5 + original teo 5 patch set
rjw-1-1 = kernel 6.19-rc5 + current teo 5 patch set
(note: Not including the most recent V2 of patch 5 of 5,
now a newer 2 patch set.)
menu = kernel 6.19-rc5
menu-rjw = kernel 6.19-rc5 + this patch.
disable = all idle states except state 0 disabled, as a reference plot, at the cost of energy.


Download attachment "misses.png" of type "image/png" (41201 bytes)

Download attachment "loop-times.png" of type "image/png" (49731 bytes)