linux-kernel - Re: [PATCH v3 4/6] perf/util/session: Replace MAX_NR_CPUS with nr_cpus

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Date:   Tue, 20 Aug 2019 11:18:52 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Kyle Meyer <meyerk@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org,
        Russ Anderson <russ.anderson@....com>,
        Kyle Meyer <kyle.meyer@....com>
Subject: Re: [PATCH v3 4/6] perf/util/session: Replace MAX_NR_CPUS with
 nr_cpus_online

On Mon, Aug 19, 2019 at 03:23:33PM -0500, Kyle Meyer wrote:
> nr_cpus_online, the number of CPUs online during a record session, can be
> used as a dynamic alternative for MAX_NR_CPUS in perf_session__cpu_bitmap.
> 
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: Russ Anderson <russ.anderson@....com>
> Signed-off-by: Kyle Meyer <kyle.meyer@....com>
> ---
>  tools/perf/util/session.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> Index: tip/tools/perf/util/session.c
> ===================================================================
> --- tip.orig/tools/perf/util/session.c
> +++ tip/tools/perf/util/session.c
> @@ -2284,6 +2284,7 @@ int perf_session__cpu_bitmap(struct perf
>  {
>  	int i, err = -1;
>  	struct perf_cpu_map *map;
> +	int nr_cpus_online = session->header.env.nr_cpus_online;

so all those bitmaps that use this function are initialized with
MAX_NR_CPUS length, are we sure that session->header.env.nr_cpus_online
is always smaller than MAX_NR_CPUS?

jirka

>  
>  	for (i = 0; i < PERF_TYPE_MAX; ++i) {
>  		struct evsel *evsel;
> @@ -2308,9 +2309,8 @@ int perf_session__cpu_bitmap(struct perf
>  	for (i = 0; i < map->nr; i++) {
>  		int cpu = map->map[i];
>  
> -		if (cpu >= MAX_NR_CPUS) {
> -			pr_err("Requested CPU %d too large. "
> -			       "Consider raising MAX_NR_CPUS\n", cpu);
> +		if (cpu >= nr_cpus_online) {
> +			pr_err("Requested CPU %d too large\n", cpu);
>  			goto out_delete_map;
>  		}
>