linux-kernel - Re: [PATCH v2 1/5] PM: domains: Add GENPD_FLAG_RT_SAFE for PREEMPT

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Message-ID: <8f37d1cc-41d9-ad4b-ec84-708f1db03e89@linaro.org>
Date:   Thu, 12 Jan 2023 12:27:40 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Adrien Thierry <athierry@...hat.com>,
        Brian Masney <bmasney@...hat.com>,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v2 1/5] PM: domains: Add GENPD_FLAG_RT_SAFE for PREEMPT_RT

On 12/01/2023 11:36, Sebastian Andrzej Siewior wrote:
> On 2023-01-06 15:52:57 [+0100], Krzysztof Kozlowski wrote:
>>> Just so I don't get this wrong, since the cpuidle-psci also calls
>>> pm_runtime_* functions so it isn't PREEMPT_RT safe, at least not yet?
>>
>> You are correct. Patch 3 here addresses it by... just not doing runtime
>> PM. This is a hacky workaround but:
>> 1. I don't have any other idea,
>> 2. It's not a big problem because RT systems are not supposed to have
>> any CPU idle (one of first things during RT system tuning is to disable
>> cpuidle).
> 
> so you say you use idle=poll instead? 

This was generic comment that system is not supposed to go into deeper
idle states.

Best regards,
Krzysztof