Re: [PATCH v2 5/5] perf/x86/amd/power: Add AMD accumulated power reporting mechanism

Borislav Petkov
2016-01-21T17:00:31Z

On Thu, Jan 21, 2016 at 04:10:40PM +0100, Peter Zijlstra wrote:
> > > > + cpumask_clear(pmu->mask);
> > > > + cpumask_clear(pmu->tmp_mask);
> > > >
> > > > for (i = 0; i < cores_per_cu; i++)
> > > > + cpumask_set_cpu(i, pmu->mask);
> > > >
> > > > + cpumask_shift_left(pmu->mask, pmu->mask, cu * cores_per_cu);
> > >
> > > Couldn't you simply use topology_sibling_cpumask(cpu) instead?
> > >
> >
> > Looks like we couldn't. That's because cores number per cu (compute
> > unit) is got by CPUID 0x8000001e EBX. That relies on the CPU hardware.
>
> Borislav? I thought the AMD compute unit stuff was modeled as the SMT
> topology.

I would think so too:

smp_num_siblings = ((ebx >> 8) & 3) + 1;

gets set based on that CPUID leaf above. And that value is
CoresPerComputeUnit which needs to be incremented by 1 to get the actual
count of cores in a compute unit.

And that participates in the setting of topology_sibling_cpumask() in
set_cpu_sibling_map().

And that looks correct on my system here:

$ grep -EriIn . /sys/devices/system/cpu/cpu?/topology/* | grep thread_siblings
/sys/devices/system/cpu/cpu0/topology/thread_siblings:1:03
/sys/devices/system/cpu/cpu0/topology/thread_siblings_list:1:0-1
/sys/devices/system/cpu/cpu1/topology/thread_siblings:1:03
/sys/devices/system/cpu/cpu1/topology/thread_siblings_list:1:0-1
/sys/devices/system/cpu/cpu2/topology/thread_siblings:1:0c
/sys/devices/system/cpu/cpu2/topology/thread_siblings_list:1:2-3
/sys/devices/system/cpu/cpu3/topology/thread_siblings:1:0c
/sys/devices/system/cpu/cpu3/topology/thread_siblings_list:1:2-3
/sys/devices/system/cpu/cpu4/topology/thread_siblings:1:30
/sys/devices/system/cpu/cpu4/topology/thread_siblings_list:1:4-5
/sys/devices/system/cpu/cpu5/topology/thread_siblings:1:30
/sys/devices/system/cpu/cpu5/topology/thread_siblings_list:1:4-5
/sys/devices/system/cpu/cpu6/topology/thread_siblings:1:c0
/sys/devices/system/cpu/cpu6/topology/thread_siblings_list:1:6-7
/sys/devices/system/cpu/cpu7/topology/thread_siblings:1:c0
/sys/devices/system/cpu/cpu7/topology/thread_siblings_list:1:6-7

and when we look at what CPUID reports:

$ cpuid -r | grep -E "^\s+0x8000001e" | awk '{ print $4 }'
ebx=0x00000100
ebx=0x00000100
ebx=0x00000101
ebx=0x00000101
ebx=0x00000102
ebx=0x00000102
ebx=0x00000103
ebx=0x00000103

We see that [15:8] is CoresPerComputeUnit which is + 1, so 2 cores per
compute unit.

And slice [7:0] gives the compute unit (CU) id of each core, so cores 0
and 1 are CU0, 2 and 3 are CU1 and so on...

So Rui, why do you say you can't use topology_sibling_cpumask()?

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.