linux-kernel - Re: [PATCH v7 1/4] cpu/SMT: Provide a default topology_is_primary

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Message-ID: <87ttcty71m.ffs@tglx>
Date: Wed, 30 Oct 2024 15:55:17 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Yicong Yang <yangyicong@...wei.com>, catalin.marinas@....com,
 will@...nel.org, sudeep.holla@....com, peterz@...radead.org,
 mpe@...erman.id.au, linux-arm-kernel@...ts.infradead.org,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
 pierre.gondois@....com, dietmar.eggemann@....com
Cc: linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
 linux-kernel@...r.kernel.org, morten.rasmussen@....com, msuchanek@...e.de,
 gregkh@...uxfoundation.org, rafael@...nel.org,
 jonathan.cameron@...wei.com, prime.zeng@...ilicon.com,
 linuxarm@...wei.com, yangyicong@...ilicon.com, xuwei5@...wei.com,
 guohanjun@...wei.com
Subject: Re: [PATCH v7 1/4] cpu/SMT: Provide a default
 topology_is_primary_thread()

On Wed, Oct 30 2024 at 20:54, Yicong Yang wrote:
>  
> +#ifndef topology_is_primary_thread
> +#define topology_is_primary_thread topology_is_primary_thread

Please do not glue defines and functions together w/o a newline in between.

> +static inline bool topology_is_primary_thread(unsigned int cpu)
> +{
> +	/*
> +	 * On SMT hotplug the primary thread of the SMT won't be disabled.
> +	 * Architectures do have a special primary thread (e.g. x86) need
> +	 * to override this function. Otherwise just make the first thread
> +	 * in the SMT as the primary thread.
> +	 */
> +	return cpu == cpumask_first(topology_sibling_cpumask(cpu));

How is that supposed to work? Assume both siblings are offline, then the
sibling mask is empty and you can't boot the CPU anymore.

Thanks,

        tglx