linux-kernel - Re: [PATCH] arm64: acpi: reenumerate topology ids

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Message-ID: <20180628173243.obydzakh2stfs26w@kamzik.brq.redhat.com>
Date:   Thu, 28 Jun 2018 19:32:43 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        jeremy.linton@....com, ard.biesheuvel@...aro.org,
        shunyong.yang@...-semitech.com, yu.zheng@...-semitech.com,
        catalin.marinas@....com, will.deacon@....com
Subject: Re: [PATCH] arm64: acpi: reenumerate topology ids

On Thu, Jun 28, 2018 at 05:30:51PM +0100, Sudeep Holla wrote:
> I am not sure if we can ever guarantee that DT and ACPI will get the
> same ids whatever counter we use as it depends on the order presented in
> the firmware(DT or ACPI). So I am not for generating ids for core and
> threads in that way.

I don't believe we have to guarantee that the exact (package,core,thread)
triplet describing a PE with DT matches ACPI. We just need to guarantee
that each triplet we select properly puts a PE in the same group as its
peers. So, as long as we keep the grouping described by DT or ACPI, then
the (package,core,thread) IDs assigned are pretty arbitrary.

I could change the commit message to state we can generate IDs *like*
DT does (i.e. with counters), even if they may not result in identical
triplet to PE mappings.

> 
> So I would like to keep it simple and just have this counters for
> package ids as demonstrated in Shunyong's patch.
> 

If we don't also handle cores when there are threads, then the cores
will also end up having weird IDs.

Thanks,
drew