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

[Conor.Dooley]

On 11/07/2022 15:59, Sudeep Holla wrote:
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> 
> On Sat, Jul 09, 2022 at 04:23:55PM +0100, Conor Dooley wrote:
>> From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxx
>> Fixes: 03f11f03dbfe ("RISC-V: Parse cpu topology during boot.")
>> Reported-by: Brice Goglin <Brice.Goglin@xxxxxxxx>
>> Link: https://github.com/open-mpi/hwloc/issues/536
>> Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>> ---
>> ---
>>  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.