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RE: [PATCH v3 2/3] xen/sched: Link CPU topology to scheduler
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>
- Date: Wed, 1 Jul 2026 21:50:47 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Timothy Pearson <tpearson@xxxxxxxxxxxxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 01 Jul 2026 21:51:05 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHdCBJhHN8gTC0+5k6Ik1hF9MtBXrZWrIoAgAKKNXA=
- Thread-topic: [PATCH v3 2/3] xen/sched: Link CPU topology to scheduler
Hello,
> > +#include <xen/cpu-topology.h>
> > #include <xen/errno.h>
> > #include <xen/init.h>
> > #include <xen/lib.h>
> > @@ -37,6 +38,8 @@ static unsigned int cpu_nr_siblings(unsigned int cpu)
> > {
> > #ifdef CONFIG_X86
> > return cpu_data[cpu].x86_num_siblings;
> > +#elif defined(CONFIG_CPU_TOPOLOGY)
> > + return cpu_topology ? cpu_topology[cpu].num_siblings : 1;
>
> See my earlier remark regarding the ordering here.
>
> > --- a/xen/common/sysctl.c
> > +++ b/xen/common/sysctl.c
> > @@ -28,6 +28,7 @@
> > #include <xen/pmstat.h>
> > #include <xen/livepatch.h>
> > #include <xen/coverage.h>
> > +#include <xen/cpu-topology.h>
>
> Taking e.g. this #include, ...
>
> > --- a/xen/include/xen/cpu-topology.h
> > +++ b/xen/include/xen/cpu-topology.h
> > @@ -9,6 +9,10 @@ struct cpu_topology {
> > cpumask_var_t thread_sibling;
> > cpumask_var_t core_sibling;
> > cpumask_var_t cluster_sibling;
> > + unsigned int phys_core_id;
> > + unsigned int phys_cluster_id;
> > + unsigned int phys_socket_id;
> > + unsigned int num_siblings;
> > };
> >
> > #ifdef CONFIG_CPU_TOPOLOGY
> > @@ -16,11 +20,22 @@ struct cpu_topology {
> > extern struct cpu_topology *cpu_topology;
> > void init_cpu_topology(void);
> >
> > +#define cpu_to_core(cpu) (cpu_topology ?
> cpu_topology[cpu].phys_core_id : 0)
> > +#define cpu_to_socket(cpu) (cpu_topology ?
> cpu_topology[cpu].phys_socket_id : 0)
> > +
> > #else /* CONFIG_CPU_TOPOLOGY */
> >
> > #define cpu_topology ((struct cpu_topology *)NULL)
> > static inline void init_cpu_topology(void) {}
> >
> > +#ifndef cpu_to_core
> > +#define cpu_to_core(cpu) (0)
> > +#endif
> > +
> > +#ifndef cpu_to_socket
> > +#define cpu_to_socket(cpu) (0)
> > +#endif
>
> ... what guarantees, on x86, that cpu_to_core and cpu_to_socket are already
> #define-d by this point, so that these fallbacks don't take effect there?
> (IOW I think you need to explicitly "#include <asm/processor.h>" below the
> #else here. Yet better might be to move those two x86 #define-s to a new
> asm/topology.h.)
You are completely right. I will fix it in v4.
Thank you,
Hirokazu Takahashi.
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