Re: [Xen-devel] [PATCH v7 01/14] x86: add socket_to_cpumask

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.05.15 at 08:47, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
> On Tue, May 19, 2015 at 07:28:49AM +0100, Jan Beulich wrote:
>> >>> On 19.05.15 at 08:12, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>> > On Mon, May 18, 2015 at 02:21:40PM +0100, Jan Beulich wrote:
>> >> >>> On 08.05.15 at 10:56, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>> >> > @@ -112,6 +115,8 @@ static int __devinit MP_processor_info_x(struct 
> mpc_config_processor *m,
>> >> >  {
>> >> >         int ver, apicid, cpu = 0;
>> >> >         
>> >> > +       total_cpus++;
>> >> > +
>> >> >         if (!(m->mpc_cpuflag & CPU_ENABLED)) {
>> >> >                 if (!hotplug)
>> >> >                         ++disabled_cpus;
>> >> 
>> >> Is there a reason you can't use disabled_cpus and avoid adding yet
>> >> another variable?
>> > 
>> > The problem is not with disabled_cpus but with num_processors, which
>> > does not keep the original detected cpus in current code.
>> > Hence 'total_cpus = disabled_cpus + num_processors' may not be correct
>> > in some cases.
>> 
>> Please be more specific about when this is a problem (I do note that
>> I'm aware that the equation will not always hold, but during my
>> inspection while reviewing your change I didn't see that this would
>> ever become problematic).
> 
> What I really need is the original cpu count enumerated from MADT. If
> not introduce total_cpus then the only way getting it AFAICS is
> 'disabled_cpus + num_processors'.
> 
> The problem is that MP_processor_info_x() have some earlier returns
> before increasing num_processors. In those cases, the cpu detected will
> neither counted to disabled_cpus nor num_processors, which means
> 'disabled_cpus + num_processors' is potentially small than what I need.

As said - I understand this. But you still fail to explain under what
(realistic, i.e. other than someone bogusly setting NR_CPUS=1)
conditions this ends up being a problem.

Jan


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