Re: [PATCH] arch_topology: Make cluster topology span at least SMT CPUs

Yicong Yang
2022-08-23T16:36:19Z

On 2022/8/23 16:06, Ionela Voinescu wrote:
> Hi Yicong,
>
> On Tuesday 23 Aug 2022 at 15:30:44 (+0800), Yicong Yang wrote:
>> From: Yicong Yang <yangyicong@hisilicon.com>
>>
>> Currently cpu_clustergroup_mask() will return CPU mask if cluster span
>> more or the same CPUs as cpu_coregroup_mask(). This will result topology
>> borken on non-Cluster SMT machines.
>
> Might be worth adding here:.. "when building with CONFIG_SCHED_CLUSTER=y"
>

will add this qualifier. thanks.

>>
>
> I thought I had covered this case, but I think I had considered LLC
> spanning more than one core (tested on TX2 as well).
>
> So you'd only hit this if LLC and cluster level span the same cores (a
> single core in this case, for non-cluster), in the presence of SMT.
>

Not sure I understand it correctly but in the below case I think the LLC may span
the same core with socket?

> Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>
>
> Many thanks,
> Ionela.
>
>> Test with:
>> qemu-system-aarch64 -enable-kvm -machine virt \
>> -net none \
>> -cpu host \
>> -bios ./QEMU_EFI.fd \
>> -m 2G \
>> -smp 48,sockets=2,cores=12,threads=2 \
>> -kernel $Image \
>> -initrd $Rootfs \
>> -nographic
>> -append "rdinit=init console=ttyAMA0 sched_verbose loglevel=8"
>>
>> We'll get below error:
>> [ 3.084568] BUG: arch topology borken
>> [ 3.084570] the SMT domain not a subset of the CLS domain
>>
>> Since cluster is a level higher than SMT, fix this by making cluster
>> spans at least SMT CPUs.
>>
>> Cc: Sudeep Holla <sudeep.holla@arm.com>
>> Cc: Vincent Guittot <vincent.guittot@linaro.org>
>> Cc: Ionela Voinescu <ionela.voinescu@arm.com>
>> Fixes: bfcc4397435d ("arch_topology: Limit span of cpu_clustergroup_mask()")
>> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
>> ---
>> drivers/base/arch_topology.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>> index 0424b59b695e..0056a1273275 100644
>> --- a/drivers/base/arch_topology.c
>> +++ b/drivers/base/arch_topology.c
>> @@ -724,7 +724,7 @@ const struct cpumask *cpu_clustergroup_mask(int cpu)
>> */
>> if (cpumask_subset(cpu_coregroup_mask(cpu),
>> &cpu_topology[cpu].cluster_sibling))
>> - return get_cpu_mask(cpu);
>> + return cpu_smt_mask(cpu);
>>
>> return &cpu_topology[cpu].cluster_sibling;
>> }
>> --
>> 2.24.0
>>
>
> .
>