linux-kernel - Re: [PATCH v5 1/4] cpu/SMT: Provide a default topology_is_primary

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Message-ID: <9c46d5f0-f4ff-461b-b483-840fab6dfecc@arm.com>
Date: Fri, 16 Aug 2024 17:54:39 +0200
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Yicong Yang <yangyicong@...wei.com>, catalin.marinas@....com,
 will@...nel.org, sudeep.holla@....com, 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
Cc: linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
 linux-kernel@...r.kernel.org, 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 v5 1/4] cpu/SMT: Provide a default
 topology_is_primary_thread()

On 06/08/2024 10:53, 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.

IMHO, ARM64 (/ARM), RISCV and PARISC (SMP) use GENERIC_ARCH_TOPOLOGY
(and drivers/base/arch_topology.c) so they could share
topology_is_primary_thread() also there?

[...]