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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.06.15 at 08:35, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
> On Fri, May 29, 2015 at 09:52:03AM +0100, Jan Beulich wrote:
>> >>> On 29.05.15 at 10:28, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>> > On Fri, May 29, 2015 at 09:01:53AM +0100, Jan Beulich wrote:
>> >> >>> On 29.05.15 at 04:35, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>> >> > On Thu, May 28, 2015 at 01:38:05PM +0100, Jan Beulich wrote:
>> >> >> >>> On 21.05.15 at 10:41, <chao.p.peng@xxxxxxxxxxxxxxx> 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.

Okay. In which case - why not calculate the value there?

Jan


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