linux-kernel - Re: [PATCH] powerpc: Enable generic cpu idle-loop

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Message-ID: <875y59j80w.fsf@vajain21.in.ibm.com>
Date:   Mon, 21 Aug 2023 10:39:51 +0530
From:   Vaibhav Jain <vaibhav@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     Jonathan Corbet <corbet@....net>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [PATCH] powerpc: Enable generic cpu idle-loop

Thanks for looking at this patch Mpe.

Michael Ellerman <mpe@...erman.id.au> writes:

> Vaibhav Jain <vaibhav@...ux.ibm.com> writes:
>> This minor patch enables config option GENERIC_IDLE_POLL_SETUP for arch
>> powerpc. This should add support for kernel param 'nohlt'.
>
> Which is named after an 8086 instruction :), but oh well.
>
Thanks. This is an interesting trivia :)

>> Powerpc kernel also supports another kernel boot-time param called
>> 'powersave' which can also be used to disable all cpu idle-states and
>> forces CPU to an idle-loop similar to what cpu_idle_poll() does. This
>> patch however makes powerpc kernel-parameters better aligned to the
>> generic boot-time parameters.
>
> It would be nice if we could make our powersave=off parameter just
> enable this generic logic.
>
> Have you looked at if that's possible? At a glance it looks like it
> should be, when cpu_idle_force_poll is true do_idle() never calls
> cpuidle_idle_call(), so the cpuidle drivers are never invoked.

Thanks for suggesting this and it looks like a simple fix to arch/idle.c
code. I have posted a v2 with the needed change on the mailing list at
https://lore.kernel.org/all/20230821045928.1350893-1-vaibhav@linux.ibm.com

-- 
Cheers
~ Vaibhav