Re: [Xen-devel] [PATCH v8 03/13] x86: maintain COS to CBM mapping for each socket

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.05.15 at 04:43, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
> On Thu, May 28, 2015 at 02:17:54PM +0100, Jan Beulich wrote:
>> >>> On 21.05.15 at 10:41, <chao.p.peng@xxxxxxxxxxxxxxx> wrote:
>> > +static int cat_cpu_init(unsigned int cpu)
>> > +{
>> > +    int rc;
>> > +    const struct cpuinfo_x86 *c = cpu_data + cpu;
>> > +
>> > +    if ( !cpu_has(c, X86_FEATURE_CAT) )
>> > +        return 0;
>> > +
>> > +    if ( test_bit(cpu_to_socket(cpu), cat_socket_enable) )
>> > +        return 0;
>> > +
>> > +    if ( cpu == smp_processor_id() )
>> > +        do_cat_cpu_init(&rc);
>> > +    else
>> > +        on_selected_cpus(cpumask_of(cpu), do_cat_cpu_init, &rc, 1);
>> 
>> This now being called in the context of CPU_UP_PREPARE, I can't see
>> how this works at all: Neither would the CPU's cpu_data[] instance be
>> initialized by that time, nor would you be able to IPI that CPU, nor can I
>> see how the if() branch could ever get entered. Was this tested at all?
> 
> Ah, yes! So it sounds really a little difficult to move the memory
> allocation from CPU_STARTING to CPU_PREPARA for this case.

Not sure why you talk about memory allocation again. That should
be done in CPU_UP_PREPARE. But stuff that needs to happen on
the CPU should happen in CPU_STARTING. The memory allocation's
size depending on a CPU characteristic of course makes this a little
problematic, but (I think I said so before) since we're assuming
symmetry in many other places, I don't see anything wrong with
you assuming symmetry here too, and hence use e.g. the boot CPU's
value to determine the allocation size.

Jan


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