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

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

On Fri, May 29, 2015 at 09:06:46AM +0100, Jan Beulich wrote:
> >>> 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.

No problem, then I can just forget the support for asymmetry in XEN.

Chao

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