linux-kernel - Re: [PATCH v2 5/5] perf parse-events: Add debug dump of evlist if reordered

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Message-ID: <6ba85605-39ea-40e0-a6f6-379deec30db7@linux.intel.com>
Date: Wed, 2 Apr 2025 13:52:44 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>, 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>,
 Howard Chu <howardchu95@...il.com>,
 Dominique Martinet <asmadeus@...ewreck.org>, Levi Yun <yeoreum.yun@....com>,
 "Dr. David Alan Gilbert" <linux@...blig.org>, Andi Kleen
 <ak@...ux.intel.com>, James Clark <james.clark@...aro.org>,
 Weilin Wang <weilin.wang@...el.com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] perf parse-events: Add debug dump of evlist if
 reordered

On 2025-04-02 12:47 p.m., Ian Rogers wrote:
> Add debug verbose output to show how evsels were reordered by
> parse_events__sort_events_and_fix_groups. For example:
> ```
> $ perf record -v -e '{instructions,cycles}' true
> Using CPUID GenuineIntel-6-B7-1
> WARNING: events were regrouped to match PMUs
> evlist after sorting/fixing: '{cpu_atom/instructions/,cpu_atom/cycles/},{cpu_core/instructions/,cpu_core/cycles/}'
> ```
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/parse-events.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 5152fd5a6ead..0f8fd5bee3a7 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -28,6 +28,7 @@
>  #include "util/evsel_config.h"
>  #include "util/event.h"
>  #include "util/bpf-filter.h"
> +#include "util/stat.h"
>  #include "util/util.h"
>  #include "tracepoint.h"
>  
> @@ -2196,14 +2197,23 @@ int __parse_events(struct evlist *evlist, const char *str, const char *pmu_filte
>  	if (ret2 < 0)
>  		return ret;
>  
> -	if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus)
> -		pr_warning("WARNING: events were regrouped to match PMUs\n");
> -
>  	/*
>  	 * Add list to the evlist even with errors to allow callers to clean up.
>  	 */
>  	evlist__splice_list_tail(evlist, &parse_state.list);
>  
> +	if (ret2 && warn_if_reordered && !parse_state.wild_card_pmus) {
> +		pr_warning("WARNING: events were regrouped to match PMUs\n");
> +
> +		if (verbose > 0) {
> +			struct strbuf sb = STRBUF_INIT;
> +
> +			evlist__uniquify_name(evlist);
> +			evlist__format_evsels(evlist, &sb, 1024);

Why is the size even less than the one in pr_err?

The user probably prefer to get the complete list in the debug.

Thanks,
Kan> +			pr_debug("evlist after sorting/fixing: '%s'\n", sb.buf);
> +			strbuf_release(&sb);
> +		}
> +	}
>  	if (!ret) {
>  		struct evsel *last;
>