linux-kernel - Re: [PATCH v1 3/5] perf evlist: Refactor evlist__scnprintf

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Message-ID: <a1d59121-f56d-409d-88e9-32fe0b748aa2@linux.intel.com>
Date: Wed, 2 Apr 2025 11:25:45 -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>, Weilin Wang <weilin.wang@...el.com>,
 Levi Yun <yeoreum.yun@....com>, "Dr. David Alan Gilbert"
 <linux@...blig.org>, Andi Kleen <ak@...ux.intel.com>,
 James Clark <james.clark@...aro.org>,
 Dominique Martinet <asmadeus@...ewreck.org>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/5] perf evlist: Refactor evlist__scnprintf_evsels



On 2025-03-18 12:14 a.m., Ian Rogers wrote:
> Switch output to using a strbuf so the storage can be resized. Rename
> as scnprintf is no longer used.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/builtin-record.c |  9 ++++++---
>  tools/perf/util/evlist.c    | 19 +++++++++----------
>  tools/perf/util/evlist.h    |  3 ++-
>  3 files changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index ba20bf7c011d..cea5959adadc 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -51,6 +51,7 @@
>  #include "util/clockid.h"
>  #include "util/off_cpu.h"
>  #include "util/bpf-filter.h"
> +#include "util/strbuf.h"
>  #include "asm/bug.h"
>  #include "perf.h"
>  #include "cputopo.h"
> @@ -2784,13 +2785,15 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>  		record__auxtrace_snapshot_exit(rec);
>  
>  	if (forks && workload_exec_errno) {
> -		char msg[STRERR_BUFSIZE], strevsels[2048];
> +		char msg[STRERR_BUFSIZE];
>  		const char *emsg = str_error_r(workload_exec_errno, msg, sizeof(msg));
> +		struct strbuf sb = STRBUF_INIT;
>  
> -		evlist__scnprintf_evsels(rec->evlist, sizeof(strevsels), strevsels);
> +		evlist__format_evsels(rec->evlist, &sb);
>  
>  		pr_err("Failed to collect '%s' for the '%s' workload: %s\n",
> -			strevsels, argv[0], emsg);
> +			sb.buf, argv[0], emsg);
> +		strbuf_release(&sb);
>  		err = -1;
>  		goto out_child;
>  	}
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 49e10d6981ad..96cfc7ed1512 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -35,6 +35,7 @@
>  #include "util/util.h"
>  #include "util/env.h"
>  #include "util/intel-tpebs.h"
> +#include "util/strbuf.h"
>  #include <signal.h>
>  #include <unistd.h>
>  #include <sched.h>
> @@ -2468,23 +2469,21 @@ struct evsel *evlist__find_evsel(struct evlist *evlist, int idx)
>  	return NULL;
>  }
>  
> -int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf)
> +void evlist__format_evsels(struct evlist *evlist, struct strbuf *sb)
>  {
>  	struct evsel *evsel;
> -	int printed = 0;
> +	bool first = true;
>  
>  	evlist__for_each_entry(evlist, evsel) {
>  		if (evsel__is_dummy_event(evsel))
>  			continue;
> -		if (size > (strlen(evsel__name(evsel)) + (printed ? 2 : 1))) {
> -			printed += scnprintf(bf + printed, size - printed, "%s%s", printed ? "," : "", evsel__name(evsel));
> -		} else {
> -			printed += scnprintf(bf + printed, size - printed, "%s...", printed ? "," : "");
> -			break;
> -		}
> -	}
>  
> -	return printed;
> +		if (!first)
> +			strbuf_addch(sb, ',');
> +> +		strbuf_addstr(sb, evsel__name(evsel));

The evlist may include hundreds of events. The error msg will be too
huge for the case.

Thanks,
Kan

> +		first = false;
> +	}
>  }
>  
>  void evlist__check_mem_load_aux(struct evlist *evlist)
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index edcbf1c10e92..5fe5cfbbebb1 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -20,6 +20,7 @@ struct pollfd;
>  struct thread_map;
>  struct perf_cpu_map;
>  struct record_opts;
> +struct strbuf;
>  struct target;
>  
>  /*
> @@ -430,7 +431,7 @@ int event_enable_timer__process(struct event_enable_timer *eet);
>  
>  struct evsel *evlist__find_evsel(struct evlist *evlist, int idx);
>  
> -int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf);
> +void evlist__format_evsels(struct evlist *evlist, struct strbuf *sb);
>  void evlist__check_mem_load_aux(struct evlist *evlist);
>  void evlist__warn_user_requested_cpus(struct evlist *evlist, const char *cpu_list);
>  void evlist__uniquify_name(struct evlist *evlist);