linux-kernel - Re: [PATCH] perf mem2node: Improve warning if detected no memory nodes

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Date:   Tue, 20 Oct 2020 08:06:27 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf mem2node: Improve warning if detected no memory
 nodes

On Mon, Oct 19, 2020 at 08:36:13AM +0800, Leo Yan wrote:
> Some archs (e.g. x86 and Arm64) don't enable the configuration
> CONFIG_MEMORY_HOTPLUG by default, if this configuration is not enabled
> when build the kernel image, the SysFS for memory nodes will be missed.
> This results in perf tool has no chance to catpure the memory nodes
> information, when perf tool reports the result and detects no memory
> nodes, it outputs "assertion failed at util/mem2node.c:99".
> 
> The output log doesn't give out reason for the failure and users have no
> clue for how to fix it.  This patch changes to use explicit way for
> warning: it tells user that detected no memory nodes and suggests to
> enable CONFIG_MEMORY_HOTPLUG for kernel building.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

> ---
>  tools/perf/util/mem2node.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/mem2node.c b/tools/perf/util/mem2node.c
> index c84f5841c7ab..03a7d7b27737 100644
> --- a/tools/perf/util/mem2node.c
> +++ b/tools/perf/util/mem2node.c
> @@ -96,7 +96,8 @@ int mem2node__init(struct mem2node *map, struct perf_env *env)
>  
>  	/* Cut unused entries, due to merging. */
>  	tmp_entries = realloc(entries, sizeof(*entries) * j);
> -	if (tmp_entries || WARN_ON_ONCE(j == 0))
> +	if (tmp_entries ||
> +	    WARN_ONCE(j == 0, "No memory nodes, is CONFIG_MEMORY_HOTPLUG enabled?\n"))
>  		entries = tmp_entries;
>  
>  	for (i = 0; i < j; i++) {
> -- 
> 2.17.1
>