linux-kernel - Re: [PATCH v2 0/1] arm: topology: parse the topology from the dt

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Message-ID: <44ab835f-3456-6bd9-97e9-5936cf5372da@arm.com>
Date:   Fri, 16 Apr 2021 12:39:30 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Valentin Schneider <valentin.schneider@....com>,
        Ruifeng Zhang <ruifeng.zhang0110@...il.com>
Cc:     linux@...linux.org.uk, sudeep.holla@....com,
        Greg KH <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, a.p.zijlstra@...llo.nl,
        mingo@...nel.org, ruifeng.zhang1@...soc.com, nianfu.bai@...soc.com,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/1] arm: topology: parse the topology from the dt

On 16/04/2021 11:32, Valentin Schneider wrote:
> On 16/04/21 15:47, Ruifeng Zhang wrote:
>> For more requirements, if all cores in one physical cluster, the
>> {aff2} of all cores are the same value.
>> i.e. the sc9863a,
>> core0: 0000000081000000
>> core1: 0000000081000100
>> core2: 0000000081000200
>> core3: 0000000081000300
>> core4: 0000000081000400
>> core5: 0000000081000500
>> core6: 0000000081000600
>> core7: 0000000081000700
>>
>> According to MPIDR all cores will parse to the one cluster, but it's
>> the big.LITTLE system, it's need two logic cluster for schedule or
>> cpufreq.
>> So I think it's better to add the logic of parse topology from DT.
> 
> Ah, so it's a slightly different issue, but still one that requires a
> different means of specifying topology.

I'm confused. Do you have the MT bit set to 1 then? So the issue that
the mpidr handling in arm32's store_cpu_topology() is not correct does
not exist?

With DynamIQ you have only *one* cluster, you should also be able to run
your big.LITTLE system with only an MC sched domain.

# cat /proc/schedstat
cpu0 ....
domain0 ff ... <- MC
...

You can introduce a cpu-map to create what we called Phantom Domains in
Android products.

# cat /proc/schedstat

cpu0 ....
domain0 0f ... <- MC
domain1 ff ... < DIE

Is this what you need for your arm32 kernel system? Adding the
possibility to parse cpu-map to create Phantom Domains?