linux-kernel - Re: [RFC PATCH 1/5] cpumask: Introduce cpu parked mask

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Message-ID: <d916d3ae-afd4-4f07-a6e8-941a71cc039e@linux.ibm.com>
Date: Mon, 23 Jun 2025 13:40:00 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Yury Norov <yury.norov@...il.com>, peterz@...radead.org
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        tglx@...utronix.de, maddy@...ux.ibm.com, vschneid@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, jstultz@...gle.com,
        kprateek.nayak@....com, huschle@...ux.ibm.com, srikar@...ux.ibm.com,
        linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: Re: [RFC PATCH 1/5] cpumask: Introduce cpu parked mask



On 5/27/25 20:36, Yury Norov wrote:
> On Fri, May 23, 2025 at 11:44:44PM +0530, Shrikanth Hegde wrote:
>> CPU is said to be parked, when underlying physical CPU is not
>> available. This happens when there is contention for CPU resource in
>> para-virtualized case. One should avoid using these CPUs.
>>
>> Build and maintain this state of parked CPUs. Scheduler will use this
>> information and push the tasks out as soon as it can.
> 
> This 'parked' term sounds pretty obscured. Maybe name it in
> a positive sense, and more explicit, like cpu_paravirt_mask.
> 

I still dont know a better name. Maybe something like cpu_avoid_mask and
cpu avoid(cpu)? I would like to retain a notion that these CPU shouldn't be used
at the moment.

> Also, shouldn't this be conditional on CONFIG_PARAVIRT?
> 

I moved the uses of it under a static key which should make it a nop for
others. That keeps code relatively simpler. Hope that's ok.

> Thanks,
> Yury
>