'perf test backward' failing with older kernels, should Skip

Message ID 5775CD34.6030107@huawei.com
State New
Headers show

Commit Message

Wang Nan July 1, 2016, 1:53 a.m.
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:

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) {

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,