linux-kernel - Re: [PATCH v1 1/8] perf: Increase MAX_NR

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Message-ID: <20241206102451.GA3418674@e132581.arm.com>
Date: Fri, 6 Dec 2024 10:24:51 +0000
From: Leo Yan <leo.yan@....com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	James Clark <james.clark@...aro.org>,
	Kyle Meyer <kyle.meyer@....com>, Ben Gainey <ben.gainey@....com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/8] perf: Increase MAX_NR_CPUS to 4096

Hi Ian,

On Thu, Dec 05, 2024 at 08:40:28PM -0800, Ian Rogers wrote:
> 
> From: Kyle Meyer <kyle.meyer@....com>
> 
> Systems have surpassed 2048 CPUs. Increase MAX_NR_CPUS to 4096.
> 
> Bitmaps declared with MAX_NR_CPUS bits will increase from 256B to 512B,
> cpus_runtime will increase from 81960B to 163880B, and max_entries will
> increase from 8192B to 16384B.
> 
> Signed-off-by: Kyle Meyer <kyle.meyer@....com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/lib/perf/include/internal/cpumap.h | 2 +-
>  tools/perf/perf.h                        | 2 +-
>  tools/perf/util/bpf_skel/kwork_top.bpf.c | 4 +++-
>  3 files changed, 5 insertions(+), 3 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

This series is fine for me.  Just wandering if we can use a central
place to maintain the macro, e.g. lib/perf/include/perf/cpumap.h.  It
is pointless to define exactly same macros in different headers.  As
least, I think we can unify this except the kwork bpf program?

P.s. for dynamically allocating per CPU maps in eBPF program, we can
refer to the code samples/bpf/xdp_sample_user.c, but this is another
topic.

Thanks,
Leo

>  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 {
> diff --git a/tools/perf/util/bpf_skel/kwork_top.bpf.c b/tools/perf/util/bpf_skel/kwork_top.bpf.c
> index 594da91965a2..73e32e063030 100644
> --- a/tools/perf/util/bpf_skel/kwork_top.bpf.c
> +++ b/tools/perf/util/bpf_skel/kwork_top.bpf.c
> @@ -18,7 +18,9 @@ enum kwork_class_type {
>  };
> 
>  #define MAX_ENTRIES     102400
> -#define MAX_NR_CPUS     2048
> +#ifndef MAX_NR_CPUS
> +#define MAX_NR_CPUS     4096
> +#endif
>  #define PF_KTHREAD      0x00200000
>  #define MAX_COMMAND_LEN 16
> 
> --
> 2.47.0.338.g60cca15819-goog
> 
>