linux-kernel - Re: [PATCH v12 1/4] cpu/SMT: Provide a default topology_is_primary

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Message-ID: <Z9BLo0rDthj2NwFu@bogus>
Date: Tue, 11 Mar 2025 14:41:39 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: Yicong Yang <yangyicong@...wei.com>
Cc: <catalin.marinas@....com>, <will@...nel.org>, <tglx@...utronix.de>,
	<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>,
	<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>, <sshegde@...ux.ibm.com>
Subject: Re: [PATCH v12 1/4] cpu/SMT: Provide a default
 topology_is_primary_thread()

On Tue, Mar 11, 2025 at 03:51:40PM +0800, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@...ilicon.com>
> 
> Currently if architectures want to support HOTPLUG_SMT they need to
> provide a topology_is_primary_thread() telling the framework which
> thread in the SMT cannot offline. However arm64 doesn't have a
> restriction on which thread in the SMT cannot offline, a simplest
> choice is that just make 1st thread as the "primary" thread. So
> just make this as the default implementation in the framework and
> let architectures like x86 that have special primary thread to
> override this function (which they've already done).
> 
> There's no need to provide a stub function if !CONFIG_SMP or
> !CONFIG_HOTPLUG_SMT. In such case the testing CPU is already
> the 1st CPU in the SMT so it's always the primary thread.
>

LGTM:

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

> +	 * enabled/active. Architectures do have a special primary thread

If you respin

^^ s/do/that/ or s/do/that do/

-- 
Regards,
Sudeep