linux-kernel - Re: [PATCH RESEND] perf: Completely remove possibility to override MAX_NR

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Message-ID: <7ded6ce4-1fcb-4e2d-94ab-5c330de6aea0@csgroup.eu>
Date: Fri, 12 Sep 2025 10:32:56 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: 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>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 "Liang, Kan" <kan.liang@...ux.intel.com>, Leo Yan <leo.yan@....com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH RESEND] perf: Completely remove possibility to override
 MAX_NR_CPUS

Le 18/08/2025 à 11:57, Christophe Leroy a écrit :
> Commit 21b8732eb447 ("perf tools: Allow overriding MAX_NR_CPUS at
> compile time") added the capability to override MAX_NR_CPUS. At
> that time it was necessary to reduce the huge amount of RAM used
> by static stats variables.
> 
> But this has been unnecessary since commit 6a1e2c5c2673 ("perf stat:
> Remove a set of shadow stats static variables"), and
> commit e8399d34d568 ("libperf cpumap: Hide/reduce scope of
> MAX_NR_CPUS") broke the build in that case because it failed to
> add the guard around the new definition of MAX_NR_CPUS.
> 
> So cleanup things and remove guards completely to officialise it
> is not necessary anymore to override MAX_NR_CPUS.
> 
> Link: https://lore.kernel.org/all/8c8553387ebf904a9e5a93eaf643cb01164d9fb3.1736188471.git.christophe.leroy@csgroup.eu/
> Fixes: e8399d34d568 ("libperf cpumap: Hide/reduce scope of MAX_NR_CPUS")
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Gentle ping

Thanks
Christophe

> ---
>   tools/perf/perf.h                        | 2 --
>   tools/perf/util/bpf_skel/kwork_top.bpf.c | 2 --
>   2 files changed, 4 deletions(-)
> 
> diff --git a/tools/perf/perf.h b/tools/perf/perf.h
> index 3cb40965549f..e004178472d9 100644
> --- a/tools/perf/perf.h
> +++ b/tools/perf/perf.h
> @@ -2,9 +2,7 @@
>   #ifndef _PERF_PERF_H
>   #define _PERF_PERF_H
>   
> -#ifndef MAX_NR_CPUS
>   #define MAX_NR_CPUS			4096
> -#endif
>   
>   enum perf_affinity {
>   	PERF_AFFINITY_SYS = 0,
> diff --git a/tools/perf/util/bpf_skel/kwork_top.bpf.c b/tools/perf/util/bpf_skel/kwork_top.bpf.c
> index 73e32e063030..6673386302e2 100644
> --- a/tools/perf/util/bpf_skel/kwork_top.bpf.c
> +++ b/tools/perf/util/bpf_skel/kwork_top.bpf.c
> @@ -18,9 +18,7 @@ enum kwork_class_type {
>   };
>   
>   #define MAX_ENTRIES     102400
> -#ifndef MAX_NR_CPUS
>   #define MAX_NR_CPUS     4096
> -#endif
>   #define PF_KTHREAD      0x00200000
>   #define MAX_COMMAND_LEN 16
>