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

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

On Tue, Jun 02, 2015 at 07:57:55AM +0100, Jan Beulich wrote:
> >>> 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?

Okay, then I just need move the invocation of set_nr_sockets() from
__start_xen() to smp_prepare_cpus().

Chao

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