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

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Message-ID: <1feb896c-e2aa-2ae5-eb7e-dd28bfb40034@huawei.com>
Date: Mon, 19 Aug 2024 15:25:18 +0800
From: Yicong Yang <yangyicong@...wei.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
CC: <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>, <yangyicong@...ilicon.com>,
	<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>, <xuwei5@...wei.com>,
	<guohanjun@...wei.com>
Subject: Re: [PATCH v5 1/4] cpu/SMT: Provide a default
 topology_is_primary_thread()

On 2024/8/16 23:54, Dietmar Eggemann wrote:
> 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?
> 

I think yes, if they want to implement HOTPLUG_SMT and don't have a restriction
on the primary thread.

Thanks.