---

yaml
---
r: 234462
b: refs/heads/master
c: e603dc1
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: fbee632d0ca9f4073a3fefb9a843eac8af036b0f
+refs/heads/master: e603dc15072c7fec0ae263597e6dabc3bb4c5c5b

trunk/tools/perf/util/evsel.c

@@ -179,8 +179,19 @@ static int __perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,
 
 	for (cpu = 0; cpu < cpus->nr; cpu++) {
 		int group_fd = -1;
-
-		evsel->attr.inherit = (cpus->map[cpu] < 0) && inherit;
+		/*
+		 * Don't allow mmap() of inherited per-task counters. This
+		 * would create a performance issue due to all children writing
+		 * to the same buffer.
+		 *
+		 * FIXME:
+		 * Proper fix is not to pass 'inherit' to perf_evsel__open*,
+		 * but a 'flags' parameter, with 'group' folded there as well,
+		 * then introduce a PERF_O_{MMAP,GROUP,INHERIT} enum, and if
+		 * O_MMAP is set, emit a warning if cpu < 0 and O_INHERIT is
+		 * set. Lets go for the minimal fix first tho.
+		 */
+		evsel->attr.inherit = (cpus->map[cpu] >= 0) && inherit;
 
 		for (thread = 0; thread < threads->nr; thread++) {