linux-kernel - Re: [PATCH] cpuidle: psci: Fix cpuhotplug routine with PREEMPT

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Message-ID: <aG-40INpi05v3-fQ@bogus>
Date: Thu, 10 Jul 2025 13:57:52 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>, ulf.hansson@...aro.org,
	Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
	linux-rt-users@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Raghavendra Kakarla <quic_rkakarla@...cinc.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"open list:Real-time Linux (PREEMPT_RT)" <linux-rt-devel@...ts.linux.dev>
Subject: Re: [PATCH] cpuidle: psci: Fix cpuhotplug routine with PREEMPT_RT=y

On Thu, Jul 10, 2025 at 02:43:10PM +0200, Rafael J. Wysocki wrote:
> On Wed, Jul 9, 2025 at 5:47 PM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
> >
> > Currently cpu hotplug with the PREEMPT_RT option set in the kernel is
> > not supported because the underlying generic power domain functions
> > used in the cpu hotplug callbacks are incompatible from a lock point
> > of view. This situation prevents the suspend to idle to reach the
> > deepest idle state for the "cluster" as identified in the
> > undermentioned commit.
> >
> > Use the compatible ones when PREEMPT_RT is enabled and remove the
> > boolean disabling the hotplug callbacks with this option.
> >
> > With this change the platform can reach the deepest idle state
> > allowing at suspend time to consume less power.
> >
> > Tested-on Lenovo T14s with the following script:
> >
> > echo 0 > /sys/devices/system/cpu/cpu3/online
> > BEFORE=$(cat /sys/kernel/debug/pm_genpd/power-domain-cpu-cluster0/idle_states | grep S0 | awk '{ print $3 }') ;
> > rtcwake -s 1 -m mem;
> > AFTER=$(cat /sys/kernel/debug/pm_genpd/power-domain-cpu-cluster0/idle_states | grep S0 | awk '{ print $3 }');
> > if [ $BEFORE -lt $AFTER ]; then
> >     echo "Test successful"
> > else
> >     echo "Test failed"
> > fi
> > echo 1 > /sys/devices/system/cpu/cpu3/online
> >
> > Fixes: 1c4b2932bd62 ("cpuidle: psci: Enable the hierarchical topology for s2idle on PREEMPT_RT")
> > Cc: Raghavendra Kakarla <quic_rkakarla@...cinc.com>
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> 
> As per MAINTAINERS, this is for Ulf/Sudeep.
> 

LGTM, so

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

I still prefer to hear from Ulf who has more knowledge and hands-on experience
with s2idle + PREEMPT_RT in case I am missing something.

-- 
Regards,
Sudeep