[PATCH] perf: Increase MAX_NR_CPUS to 4096

[PATCH] perf: Increase MAX_NR_CPUS to 4096

[Kyle Meyer]

Systems have surpassed 2048 CPUs. Increase MAX_NR_CPUS to 4096.

Bitmaps declared with MAX_NR_CPUS bits will increase from 256B to 512B,
and cpus_runtime will increase from 81960B to 163880B.

Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
---

Tested on a 32 socket Sapphire Rapids system with 3840 CPUs.

 tools/lib/perf/include/internal/cpumap.h | 2 +-
 tools/perf/perf.h                        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/perf/include/internal/cpumap.h b/tools/lib/perf/include/internal/cpumap.h
index 49649eb51ce4..3cf28522004e 100644
--- a/tools/lib/perf/include/internal/cpumap.h
+++ b/tools/lib/perf/include/internal/cpumap.h
@@ -22,7 +22,7 @@ DECLARE_RC_STRUCT(perf_cpu_map) {
 };
 
 #ifndef MAX_NR_CPUS
-#define MAX_NR_CPUS	2048
+#define MAX_NR_CPUS	4096
 #endif
 
 struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus);
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index c004dd4e65a3..3cb40965549f 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -3,7 +3,7 @@
 #define _PERF_PERF_H
 
 #ifndef MAX_NR_CPUS
-#define MAX_NR_CPUS			2048
+#define MAX_NR_CPUS			4096
 #endif
 
 enum perf_affinity {
-- 
2.47.1

Re: [PATCH] perf: Increase MAX_NR_CPUS to 4096

[Ian Rogers]

On Thu, Dec 5, 2024 at 9:01 AM Kyle Meyer <kyle.meyer@hpe.com> wrote:
>
> Systems have surpassed 2048 CPUs. Increase MAX_NR_CPUS to 4096.
>
> Bitmaps declared with MAX_NR_CPUS bits will increase from 256B to 512B,
> and cpus_runtime will increase from 81960B to 163880B.
>
> Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>

This is very interesting, thanks Kyle! Just noting, having the same
#define in many places is clearly error prone and there are other
redefinitions of this value:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/bpf_skel/kwork_top.bpf.c?h=perf-tools-next#n21

I wonder I can refactor `tools/lib/perf/cpumap.c` to get rid of that
constant as it is only used when parsing from a file/string.

Could the kwork developers perhaps look at their many uses? The other
uses in the tool may be removable too.

Wrt this change, perhaps bump
`tools/perf/util/bpf_skel/kwork_top.bpf.c` too and then we merge that
while trying to remove other uses.

Thanks,
Ian




> ---
>
> Tested on a 32 socket Sapphire Rapids system with 3840 CPUs.
>
>  tools/lib/perf/include/internal/cpumap.h | 2 +-
>  tools/perf/perf.h                        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/perf/include/internal/cpumap.h b/tools/lib/perf/include/internal/cpumap.h
> index 49649eb51ce4..3cf28522004e 100644
> --- a/tools/lib/perf/include/internal/cpumap.h
> +++ b/tools/lib/perf/include/internal/cpumap.h
> @@ -22,7 +22,7 @@ DECLARE_RC_STRUCT(perf_cpu_map) {
>  };
>
>  #ifndef MAX_NR_CPUS
> -#define MAX_NR_CPUS    2048
> +#define MAX_NR_CPUS    4096
>  #endif
>
>  struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus);
> diff --git a/tools/perf/perf.h b/tools/perf/perf.h
> index c004dd4e65a3..3cb40965549f 100644
> --- a/tools/perf/perf.h
> +++ b/tools/perf/perf.h
> @@ -3,7 +3,7 @@
>  #define _PERF_PERF_H
>
>  #ifndef MAX_NR_CPUS
> -#define MAX_NR_CPUS                    2048
> +#define MAX_NR_CPUS                    4096
>  #endif
>
>  enum perf_affinity {
> --
> 2.47.1
>

Re: [PATCH] perf: Increase MAX_NR_CPUS to 4096

[Kyle Meyer]

On Thu, Dec 05, 2024 at 09:36:07AM -0800, Ian Rogers wrote:
> On Thu, Dec 5, 2024 at 9:01 AM Kyle Meyer <kyle.meyer@hpe.com> wrote:
> >
> > Systems have surpassed 2048 CPUs. Increase MAX_NR_CPUS to 4096.
> >
> > Bitmaps declared with MAX_NR_CPUS bits will increase from 256B to 512B,
> > and cpus_runtime will increase from 81960B to 163880B.
> >
> > Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
> 
> This is very interesting, thanks Kyle! Just noting, having the same
> #define in many places is clearly error prone and there are other
> redefinitions of this value:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/bpf_skel/kwork_top.bpf.c?h=perf-tools-next#n21
> 
> I wonder I can refactor `tools/lib/perf/cpumap.c` to get rid of that
> constant as it is only used when parsing from a file/string.
> 
> Could the kwork developers perhaps look at their many uses? The other
> uses in the tool may be removable too.
> 
> Wrt this change, perhaps bump
> `tools/perf/util/bpf_skel/kwork_top.bpf.c` too and then we merge that
> while trying to remove other uses.

Sure, that sounds good to me. I'll send a second version.

Thanks,
Kyle Meyer

> > ---
> >
> > Tested on a 32 socket Sapphire Rapids system with 3840 CPUs.
> >
> >  tools/lib/perf/include/internal/cpumap.h | 2 +-
> >  tools/perf/perf.h                        | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/lib/perf/include/internal/cpumap.h b/tools/lib/perf/include/internal/cpumap.h
> > index 49649eb51ce4..3cf28522004e 100644
> > --- a/tools/lib/perf/include/internal/cpumap.h
> > +++ b/tools/lib/perf/include/internal/cpumap.h
> > @@ -22,7 +22,7 @@ DECLARE_RC_STRUCT(perf_cpu_map) {
> >  };
> >
> >  #ifndef MAX_NR_CPUS
> > -#define MAX_NR_CPUS    2048
> > +#define MAX_NR_CPUS    4096
> >  #endif
> >
> >  struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus);
> > diff --git a/tools/perf/perf.h b/tools/perf/perf.h
> > index c004dd4e65a3..3cb40965549f 100644
> > --- a/tools/perf/perf.h
> > +++ b/tools/perf/perf.h
> > @@ -3,7 +3,7 @@
> >  #define _PERF_PERF_H
> >
> >  #ifndef MAX_NR_CPUS
> > -#define MAX_NR_CPUS                    2048
> > +#define MAX_NR_CPUS                    4096
> >  #endif
> >
> >  enum perf_affinity {
> > --
> > 2.47.1
> >