perf evsel: Fix write_backwards fallback

Commit b90dc17a5d14 "perf evsel: Add overwrite attribute and check
write_backward" misunderstood the 'order' should be obeyed in
__perf_evsel__open.

But the way this was done for attr.write_backwards was buggy, as we need
to check features in the inverse order of their introduction to the
kernel, so that a newer tool checks first the newest perf_event_attr
fields, detecting that the older kernel doesn't have support for them.

Also, we can avoid calling sys_perf_event_open() if we have already
detected the missing of write_backward.

Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Fixes: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward")
Link: http://lkml.kernel.org/r/1466419645-75551-2-git-send-email-wangnan0@huawei.com
Link: http://lkml.kernel.org/r/20160616214724.GI13337@kernel.org
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9b2e3e6..1d8f2bb 100644 (file)
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1389,8 +1389,11 @@ fallback_missing_features:
        if (perf_missing_features.lbr_flags)
                evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
                                     PERF_SAMPLE_BRANCH_NO_CYCLES);
-       if (perf_missing_features.write_backward)
+       if (perf_missing_features.write_backward) {
+               if (evsel->overwrite)
+                       return -EINVAL;
                evsel->attr.write_backward = false;
+       }
 retry_sample_id:
        if (perf_missing_features.sample_id_all)
                evsel->attr.sample_id_all = 0;
@@ -1453,12 +1456,6 @@ retry_open:
                                err = -EINVAL;
                                goto out_close;
                        }
-
-                       if (evsel->overwrite &&
-                           perf_missing_features.write_backward) {
-                               err = -EINVAL;
-                               goto out_close;
-                       }
                }
        }
 
@@ -1496,7 +1493,10 @@ try_fallback:
         * Must probe features in the order they were added to the
         * perf_event_attr interface.
         */
-       if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
+       if (!perf_missing_features.write_backward && evsel->attr.write_backward) {
+               perf_missing_features.write_backward = true;
+               goto fallback_missing_features;
+       } else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {
                perf_missing_features.clockid_wrong = true;
                goto fallback_missing_features;
        } else if (!perf_missing_features.clockid && evsel->attr.use_clockid) {
@@ -1521,12 +1521,7 @@ try_fallback:
                          PERF_SAMPLE_BRANCH_NO_FLAGS))) {
                perf_missing_features.lbr_flags = true;
                goto fallback_missing_features;
-       } else if (!perf_missing_features.write_backward &&
-                       evsel->attr.write_backward) {
-               perf_missing_features.write_backward = true;
-               goto fallback_missing_features;
        }
-
 out_close:
        do {
                while (--thread >= 0) {
@@ -2409,6 +2404,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
        "We found oprofile daemon running, please stop it and try again.");
                break;
        case EINVAL:
+               if (evsel->overwrite && perf_missing_features.write_backward)
+                       return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel.");
                if (perf_missing_features.clockid)
                        return scnprintf(msg, size, "clockid feature not supported.");
                if (perf_missing_features.clockid_wrong)