linux-kernel - [PATCH v1 4/4] perf inject: Lazily allocate guest_event event

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Message-Id: <20230527034324.2597593-5-irogers@google.com>
Date:   Fri, 26 May 2023 20:43:22 -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>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1 4/4] perf inject: Lazily allocate guest_event event_buf

The event_buf is 64kb (PERF_SAMPLE_SIZE_MAX) and stack allocated in
struct perf_inject. It is used for guest events that may not exist in
a file. Make the array allocation lazy to cut down on the stack usage.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/builtin-inject.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
index da8c89fefa3a..d68d25575b6c 100644
--- a/tools/perf/builtin-inject.c
+++ b/tools/perf/builtin-inject.c
@@ -47,7 +47,7 @@
 struct guest_event {
 	struct perf_sample		sample;
 	union perf_event		*event;
-	char				event_buf[PERF_SAMPLE_MAX_SIZE];
+	char				*event_buf;
 };
 
 struct guest_id {
@@ -1372,11 +1372,19 @@ static void guest_session__convert_time(struct guest_session *gs, u64 guest_time
 
 static int guest_session__fetch(struct guest_session *gs)
 {
-	void *buf = gs->ev.event_buf;
-	struct perf_event_header *hdr = buf;
+	void *buf;
+	struct perf_event_header *hdr;
 	size_t hdr_sz = sizeof(*hdr);
 	ssize_t ret;
 
+	buf = gs->ev.event_buf;
+	if (!buf) {
+		buf = malloc(PERF_SAMPLE_MAX_SIZE);
+		if (!buf)
+			return -ENOMEM;
+		gs->ev.event_buf = buf;
+	}
+	hdr = buf;
 	ret = readn(gs->tmp_fd, buf, hdr_sz);
 	if (ret < 0)
 		return ret;
@@ -2399,5 +2407,6 @@ int cmd_inject(int argc, const char **argv)
 		perf_data__close(&inject.output);
 	free(inject.itrace_synth_opts.vm_tm_corr_args);
 	free(inject.event_copy);
+	free(inject.guest_session.ev.event_buf);
 	return ret;
 }
-- 
2.41.0.rc0.172.g3f132b7071-goog