On Wed, Jul 07, 2021 at 02:43:07PM -0300, Arnaldo Carvalho de Melo wrote:

Em Tue, Jul 06, 2021 at 05:17:03PM +0200, Jiri Olsa escreveu:

quoted

Adding support to set group_fd in perf_evsel__open
call and make it to follow the group setup.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/perf/evsel.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
index 3e6638d27c45..9ebf7122d476 100644
--- a/tools/lib/perf/evsel.c
+++ b/tools/lib/perf/evsel.c

@@ -17,6 +17,7 @@
 #include <linux/string.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <asm/bug.h>
 
 void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr,
 		      int idx)

@@ -76,6 +77,25 @@ sys_perf_event_open(struct perf_event_attr *attr,
 	return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
 }
 
+static int get_group_fd(struct perf_evsel *evsel, int cpu, int thread)
+{
+	struct perf_evsel *leader = evsel->leader;
+	int fd;
+
+	if (evsel == leader)
+		return -1;
+
+	/*
+	 * Leader must be already processed/open,
+	 * if not it's a bug.
+	 */
+	BUG_ON(!leader->fd);

Humm, having panics in library code looks ugly, why can't we just return
some errno and let the whatever is using the library to fail gracefully?

true, I took it from perf code, did not realize this,
I'll check what can we do in ehre

I applied the patches so far, will make them available at tmp.perf/core
now.

great, I'll take the patches from there for my next change

thanks,
jirka

- Arnaldo

quoted

+	fd = FD(leader, cpu, thread);
+	BUG_ON(fd == -1);
+	return fd;
+}
+
 int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
 		     struct perf_thread_map *threads)
 {

@@ -111,11 +131,13 @@ int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
 
 	for (cpu = 0; cpu < cpus->nr; cpu++) {
 		for (thread = 0; thread < threads->nr; thread++) {
-			int fd;
+			int fd, group_fd;
+
+			group_fd = get_group_fd(evsel, cpu, thread);
 
 			fd = sys_perf_event_open(&evsel->attr,
 						 threads->map[thread].pid,
-						 cpus->map[cpu], -1, 0);
+						 cpus->map[cpu], group_fd, 0);
 
 			if (fd < 0)
 				return -errno;

-- 
2.31.1

-- 

- Arnaldo