Re: [PATCH 7/7] perf/x86/intel/P4: Fix smp_num_siblings usage

Peter Zijlstra
2022-08-16T10:18:23Z

On Tue, Aug 16, 2022 at 10:26:19AM +0800, Zhang Rui wrote:
> On Mon, 2022-08-15 at 11:11 +0200, Peter Zijlstra wrote:
> > On Sat, Aug 13, 2022 at 12:41:44AM +0800, Zhang Rui wrote:
> > > smp_num_siblings can be larger than 2.
> >
> > Not on a P4 it can't ;-)
>
> Kernel code doesn't prevent this from happening, so it just depends on
> how SMT ID is encoded in APICID.

No P4 ever encountered had it different and since no P4 will ever be
made again (I sincerely hope) we have a complete case.

> Checking for smp_num_sibling > 1 is the right logic to detect HT
> support, which is followed by all other kernel code except this one. :)

I'm fine with making it consistent, I'm arguing with the subject calling
this a fix, it is not, it's a functional no-op.