linux-kernel - Re: [PATCH v3 2/2] riscv: topology: fix default topology reporting

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Message-ID: <6f96ad4b-6901-d5fd-9d55-2da9bdc925c3@microchip.com>
Date:   Mon, 11 Jul 2022 16:28:28 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <sudeep.holla@....com>, <mail@...chuod.ie>
CC:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <palmer@...osinc.com>, <aou@...s.berkeley.edu>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <gregkh@...uxfoundation.org>, <rafael@...nel.org>,
        <Daire.McNamara@...rochip.com>, <niklas.cassel@....com>,
        <damien.lemoal@...nsource.wdc.com>, <geert@...ux-m68k.org>,
        <zong.li@...ive.com>, <kernel@...il.dk>, <hahnjo@...njo.de>,
        <guoren@...nel.org>, <anup@...infault.org>,
        <atishp@...shpatra.org>, <heiko@...ech.de>,
        <philipp.tomsich@...ll.eu>, <robh@...nel.org>, <maz@...nel.org>,
        <viresh.kumar@...aro.org>, <linux-riscv@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <Brice.Goglin@...ia.fr>
Subject: Re: [PATCH v3 2/2] riscv: topology: fix default topology reporting

On 11/07/2022 15:59, Sudeep Holla wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Sat, Jul 09, 2022 at 04:23:55PM +0100, Conor Dooley wrote:
>> From: Conor Dooley <conor.dooley@...rochip.com>
>>
>> RISC-V has no sane defaults to fall back on where there is no cpu-map
>> in the devicetree.
>> Without sane defaults, the package, core and thread IDs are all set to
>> -1. This causes user-visible inaccuracies for tools like hwloc/lstopo
>> which rely on the sysfs cpu topology files to detect a system's
>> topology.
>>
>> On a PolarFire SoC, which should have 4 harts with a thread each,
>> lstopo currently reports:
>>
>> Machine (793MB total)
>>   Package L#0
>>     NUMANode L#0 (P#0 793MB)
>>     Core L#0
>>       L1d L#0 (32KB) + L1i L#0 (32KB) + PU L#0 (P#0)
>>       L1d L#1 (32KB) + L1i L#1 (32KB) + PU L#1 (P#1)
>>       L1d L#2 (32KB) + L1i L#2 (32KB) + PU L#2 (P#2)
>>       L1d L#3 (32KB) + L1i L#3 (32KB) + PU L#3 (P#3)
>>
>> Adding calls to store_cpu_topology() in {boot,smp} hart bringup code
>> results in the correct topolgy being reported:
>>
>> Machine (793MB total)
>>   Package L#0
>>     NUMANode L#0 (P#0 793MB)
>>     L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 + PU L#0 (P#0)
>>     L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 + PU L#1 (P#1)
>>     L1d L#2 (32KB) + L1i L#2 (32KB) + Core L#2 + PU L#2 (P#2)
>>     L1d L#3 (32KB) + L1i L#3 (32KB) + Core L#3 + PU L#3 (P#3)
>>
>> CC: stable@...r.kernel.org
>> Fixes: 03f11f03dbfe ("RISC-V: Parse cpu topology during boot.")
>> Reported-by: Brice Goglin <Brice.Goglin@...ia.fr>
>> Link: https://github.com/open-mpi/hwloc/issues/536
>> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
>> ---
>> ---
>>  arch/riscv/Kconfig          | 2 +-
>>  arch/riscv/kernel/smpboot.c | 4 +++-
>>  2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 2af0701b7518..4b6c2fdbb57c 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -52,7 +52,7 @@ config RISCV
>>       select COMMON_CLK
>>       select CPU_PM if CPU_IDLE
>>       select EDAC_SUPPORT
>> -     select GENERIC_ARCH_TOPOLOGY if SMP
>> +     select GENERIC_ARCH_TOPOLOGY
> 
> I am not sure of !SMP as ARM64 is default SMP only. I have never reviewed
> the arch topology code with !SMP considered. I will leave that part to
> RISC-V developers.
> 

I checked it on a D1 which is !SMP - no trouble booting and
the topology reporting seemed fine.

Thanks for the reviews,
Conor.