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

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Message-ID: <CAPDyKFo6hE9BPgS7Bhe259Mxki-KBZDYyMkaBPFuznETbZhGkQ@mail.gmail.com>
Date: Tue, 9 Jul 2024 17:31:12 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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 Mon, 8 Jul 2024 at 15:53, Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> 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 ;)

Thanks for taking a look and for providing your thoughts. Can I
consider that as an "ack" for the whole series?

Before I decide to apply this I am awaiting some additional
confirmation from Qcom guys. It's getting late for v6.11, so I may
need to make another re-spin, but let's see.

Kind regards
Uffe