linux-kernel - [PATCH v2 03/16] perf parse-events: Avoid copying an empty list

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Date: Mon, 15 Apr 2024 23:15:19 -0700
From: Ian Rogers <irogers@...gle.com>
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>, 
	Kan Liang <kan.liang@...ux.intel.com>, James Clark <james.clark@....com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, Atish Patra <atishp@...osinc.com>, linux-riscv@...ts.infradead.org, 
	Beeman Strong <beeman@...osinc.com>
Subject: [PATCH v2 03/16] perf parse-events: Avoid copying an empty list

In parse_events_add_pmu, delay copying the list of terms until it is
known the list contains terms.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/parse-events.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 2d5a275dd257..3b1f767039fa 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1398,29 +1398,21 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 	struct parse_events_terms parsed_terms;
 	bool alias_rewrote_terms = false;
 
-	parse_events_terms__init(&parsed_terms);
-	if (const_parsed_terms) {
-		int ret = parse_events_terms__copy(const_parsed_terms, &parsed_terms);
-
-		if (ret)
-			return ret;
-	}
-
 	if (verbose > 1) {
 		struct strbuf sb;
 
 		strbuf_init(&sb, /*hint=*/ 0);
-		if (pmu->selectable && list_empty(&parsed_terms.terms)) {
+		if (pmu->selectable && const_parsed_terms &&
+		    list_empty(&const_parsed_terms->terms)) {
 			strbuf_addf(&sb, "%s//", pmu->name);
 		} else {
 			strbuf_addf(&sb, "%s/", pmu->name);
-			parse_events_terms__to_strbuf(&parsed_terms, &sb);
+			parse_events_terms__to_strbuf(const_parsed_terms, &sb);
 			strbuf_addch(&sb, '/');
 		}
 		fprintf(stderr, "Attempt to add: %s\n", sb.buf);
 		strbuf_release(&sb);
 	}
-	fix_raw(&parsed_terms, pmu);
 
 	memset(&attr, 0, sizeof(attr));
 	if (pmu->perf_event_attr_init_default)
@@ -1428,7 +1420,7 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 
 	attr.type = pmu->type;
 
-	if (list_empty(&parsed_terms.terms)) {
+	if (!const_parsed_terms || list_empty(&const_parsed_terms->terms)) {
 		evsel = __add_event(list, &parse_state->idx, &attr,
 				    /*init_attr=*/true, /*name=*/NULL,
 				    /*metric_id=*/NULL, pmu,
@@ -1437,6 +1429,15 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 		return evsel ? 0 : -ENOMEM;
 	}
 
+	parse_events_terms__init(&parsed_terms);
+	if (const_parsed_terms) {
+		int ret = parse_events_terms__copy(const_parsed_terms, &parsed_terms);
+
+		if (ret)
+			return ret;
+	}
+	fix_raw(&parsed_terms, pmu);
+
 	/* Configure attr/terms with a known PMU, this will set hardcoded terms. */
 	if (config_attr(&attr, &parsed_terms, parse_state->error, config_term_pmu)) {
 		parse_events_terms__exit(&parsed_terms);
-- 
2.44.0.683.g7961c838ac-goog