[v2,11/13] libperf: Lazily allocate mmap event copy

Commit Message

Ian Rogers Oct. 12, 2023, 6:23 a.m. UTC

The event copy in the mmap is used to have storage to a read
event. Not all users of mmaps read the events, such as perf record, so
switch the allocation to being on first read rather than being
embedded within the perf_mmap.

Signed-off-by: Ian Rogers <[e-mail]>
---
 tools/lib/perf/include/internal/mmap.h | 2 +-
 tools/lib/perf/mmap.c                  | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

Patch

diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
index 5a062af8e9d8..b11aaf5ed645 100644
--- a/tools/lib/perf/include/internal/mmap.h
+++ b/tools/lib/perf/include/internal/mmap.h
@@ -33,7 +33,7 @@  struct perf_mmap {
 	bool			 overwrite;
 	u64			 flush;
 	libperf_unmap_cb_t	 unmap_cb;
-	char			 event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
+	void			*event_copy;
 	struct perf_mmap	*next;
 };
 
diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index 2184814b37dd..91ae46aac378 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c
@@ -51,6 +51,8 @@  int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
 
 void perf_mmap__munmap(struct perf_mmap *map)
 {
+	free(map->event_copy);
+	map->event_copy = NULL;
 	if (map && map->base != NULL) {
 		munmap(map->base, perf_mmap__mmap_len(map));
 		map->base = NULL;
@@ -226,6 +228,13 @@  static union perf_event *perf_mmap__read(struct perf_mmap *map,
 			unsigned int len = min(sizeof(*event), size), cpy;
 			void *dst = map->event_copy;
 
+			if (!dst) {
+				dst = malloc(PERF_SAMPLE_MAX_SIZE);
+				if (!dst)
+					return NULL;
+				map->event_copy = dst;
+			}
+
 			do {
 				cpy = min(map->mask + 1 - (offset & map->mask), len);
 				memcpy(dst, &data[offset & map->mask], cpy);