linux-kernel - Re: [PATCH v2 0/7] pmdomain/cpuidle-psci: Support s2idle/s2ram on PREEMPT

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Message-ID: <20240708135310.3VRFnmk1@linutronix.de>
Date: Mon, 8 Jul 2024 15:53:10 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Nikunj Kela <nkela@...cinc.com>,
	Prasad Sodagudi <psodagud@...cinc.com>,
	Maulik Shah <quic_mkshah@...cinc.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	linux-rt-users@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/7] pmdomain/cpuidle-psci: Support s2idle/s2ram on
 PREEMPT_RT

On 2024-05-27 16:25:50 [+0200], Ulf Hansson wrote:
> Updates in v2:
> 	- Rebased and fixed a small issue in genpd, see patch3.
> 	- Re-tested on v6.9-rt5 (PREEMPT_RT enabled)
> 	- Re-tested on v6.10-rc1 (for regressions, PREEMPT_RT disabled)
> 
> The hierarchical PM domain topology and the corresponding domain-idle-states
> are currently disabled on a PREEMPT_RT based configuration. The main reason is
> because spinlocks are turned into sleepable locks on PREEMPT_RT, which means
> genpd and runtime PM can't be use in the atomic idle-path when
> selecting/entering an idle-state.
> 
> For s2idle/s2ram this is an unnecessary limitation that this series intends to
> address. Note that, the support for cpuhotplug is left to future improvements.
> More information about this are available in the commit messages.

I looked at it and it seems limited to pmdomain/core.c, also I don't
know if there is a ->set_performance_state callback set since the one I
checked have mutex_t locking ;)
So if this is needed, then be it. s2ram wouldn't be used in "production"
but in "safe state" so I wouldn't worry too much about latency spikes.
Not sure what it means for the other modes.
I am not to worried for now, please don't let spread more than needed ;)

> Kind regards
> Ulf Hansson

Sebastian