Re: [PATCH v8 01/13] x86: add socket_cpumask

[Chao Peng <chao.p.peng@linux.intel.com>]

On Fri, May 29, 2015 at 09:52:03AM +0100, Jan Beulich wrote:
> >>> On 29.05.15 at 10:28, <chao.p.peng@linux.intel.com> wrote:
> > On Fri, May 29, 2015 at 09:01:53AM +0100, Jan Beulich wrote:
> >> >>> On 29.05.15 at 04:35, <chao.p.peng@linux.intel.com> wrote:
> >> > On Thu, May 28, 2015 at 01:38:05PM +0100, Jan Beulich wrote:
> >> >> >>> On 21.05.15 at 10:41, <chao.p.peng@linux.intel.com> wrote:
> >> >> > --- a/xen/arch/x86/mpparse.c
> >> >> > +++ b/xen/arch/x86/mpparse.c
> >> >> > @@ -87,6 +87,18 @@ void __init set_nr_cpu_ids(unsigned int max_cpus)
> >> >> >  #endif
> >> >> >  }
> >> >> >  
> >> >> > +void __init set_nr_sockets(void)
> >> >> > +{
> >> >> > +    unsigned int cpus = bitmap_weight(phys_cpu_present_map.mask,
> >> >> > +                                      boot_cpu_data.x86_max_cores *
> >> >> > +                                      boot_cpu_data.x86_num_siblings);
> >> >> > +
> >> >> > +    if ( cpus == 0 )
> >> >> > +        cpus = 1;
> >> >> > +
> >> >> > +    nr_sockets = DIV_ROUND_UP(num_processors + disabled_cpus, cpus);
> >> >> > +}
> >> >> 
> >> >> Is there a reason why this can't just be added to the end of the
> >> >> immediately preceding set_nr_cpu_ids()?
> >> > 
> >> > You mean the declaration or invocation? If the former I have no special
> >> > reason for it (e.g. I can change it).
> >> 
> >> Neither - I just don't see the need for a new function.
> > 
> > In which case the invocation of set_nr_cpu_ids() should move to the
> > place where now set_nr_sockets() is invoked, to make sure
> > boot_cpu_data.x86_max_cores/x86_num_siblings available, which may not be
> > your expectation.
> 
> Ah, in which case this _is_ the explanation, albeit only provided the
> use of the two boot_cpu_data fields has to remain (which I had put
> under question). And if these have to remain, couldn't this be done
> in a presmp initcall instead of an explicitly called function?

presmp is too late. nr_sockets will get used in smp_prepare_cpus()
before calling set_cpu_sibling_map for cpu 0.

Chao