On 2016/7/1 5:00, Arnaldo Carvalho de Melo wrote:
Hi Wang,
I booted a machine with the f24 distro kernel and the backward
ring buffer test started FAILing, when it should've noticed that the
kernel doesn't support it and Skip instead:
[root@jouet ~]# perf test -v backward
45: Test backward reading from ring buffer :
--- start ---
<SNIP>
mmap size 1052672B
Unexpected counter: sample_count=0, comm_count=0
---- end ----
Test backward reading from ring buffer: FAILED!
[root@jouet ~]#
I didn't test it on old kernel, but I tested it by forcing
sys_perf_event_open
return -EINVAL when attr->backward is true by following patch:
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1d8f2bb..3e91c63 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1418,6 +1418,9 @@ retry_open:
pr_debug2("sys_perf_event_open: pid %d cpu %d
group_fd %d flags %#lx\n",
pid, cpus->map[cpu], group_fd, flags);
+ if (evsel->attr.write_backward)
+ FD(evsel, cpu, thread) = -EINVAL;
+ else
FD(evsel, cpu, thread) =
sys_perf_event_open(&evsel->attr,
pid,
cpus->map[cpu],
'perf test' skips this test.
Let me switch to an old kernel and try again...
Oops... It does FAILED...
Seems the code I use to emulate old kernel is wrong. I should set errno
to EINVAL and
make FD(...) = -1.
I agree with your patch. Thank you for pointing it out.
Ok, so I think the patch below should do the trick, is that right? With it
I get:
[root@jouet ~]# perf test backward
45: Test backward reading from ring buffer : Skip
[root@jouet ~]#
diff --git a/tools/perf/tests/backward-ring-buffer.c
b/tools/perf/tests/backward-ring-buffer.c
index e70313fac5a5..0731b0bf9552 100644
--- a/tools/perf/tests/backward-ring-buffer.c
+++ b/tools/perf/tests/backward-ring-buffer.c
@@ -118,8 +118,10 @@ int test__backward_ring_buffer(int subtest __maybe_unused)
perf_evlist__config(evlist, &opts, NULL);
/* Set backward bit, ring buffer should be writing from end */
- evlist__for_each_entry(evlist, evsel)
+ evlist__for_each_entry(evlist, evsel) {
+ evsel->overwrite = true;
evsel->attr.write_backward = 1;
+ }
err = perf_evlist__open(evlist);
if (err < 0) {
