4 files changed, 157 insertions, 0 deletions

diff --git a/tools/perf/tests/Build b/tools/perf/tests/Build
index 449fe97a555f..66a28982547b 100644
--- a/tools/perf/tests/Build
+++ b/tools/perf/tests/Build
@@ -38,6 +38,7 @@ perf-y += cpumap.o
 perf-y += stat.o
 perf-y += event_update.o
 perf-y += event-times.o
+perf-y += backward-ring-buffer.o
 
 $(OUTPUT)tests/llvm-src-base.c: tests/bpf-script-example.c tests/Build
         $(call rule_mkdir)
diff --git a/tools/perf/tests/backward-ring-buffer.c b/tools/perf/tests/backward-ring-buffer.c
new file mode 100644
index 000000000000..d9ba991a9a30
--- /dev/null
+++ b/tools/perf/tests/backward-ring-buffer.c
@@ -0,0 +1,151 @@
+/*
+ * Test backward bit in event attribute, read ring buffer from end to
+ * beginning
+ */
+
+#include <perf.h>
+#include <evlist.h>
+#include <sys/prctl.h>
+#include "tests.h"
+#include "debug.h"
+
+#define NR_ITERS 111
+
+static void testcase(void)
+{
+        int i;
+
+        for (i = 0; i < NR_ITERS; i++) {
+                char proc_name[10];
+
+                snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
+                prctl(PR_SET_NAME, proc_name);
+        }
+}
+
+static int count_samples(struct perf_evlist *evlist, int *sample_count,
+                         int *comm_count)
+{
+        int i;
+
+        for (i = 0; i < evlist->nr_mmaps; i++) {
+                union perf_event *event;
+
+                perf_evlist__mmap_read_catchup(evlist, i);
+                while ((event = perf_evlist__mmap_read_backward(evlist, i)) != NULL) {
+                        const u32 type = event->header.type;
+
+                        switch (type) {
+                        case PERF_RECORD_SAMPLE:
+                                (*sample_count)++;
+                                break;
+                        case PERF_RECORD_COMM:
+                                (*comm_count)++;
+                                break;
+                        default:
+                                pr_err("Unexpected record of type %d\n", type);
+                                return TEST_FAIL;
+                        }
+                }
+        }
+        return TEST_OK;
+}
+
+static int do_test(struct perf_evlist *evlist, int mmap_pages,
+                   int *sample_count, int *comm_count)
+{
+        int err;
+        char sbuf[STRERR_BUFSIZE];
+
+        err = perf_evlist__mmap(evlist, mmap_pages, true);
+        if (err < 0) {
+                pr_debug("perf_evlist__mmap: %s\n",
+                         strerror_r(errno, sbuf, sizeof(sbuf)));
+                return TEST_FAIL;
+        }
+
+        perf_evlist__enable(evlist);
+        testcase();
+        perf_evlist__disable(evlist);
+
+        err = count_samples(evlist, sample_count, comm_count);
+        perf_evlist__munmap(evlist);
+        return err;
+}
+
+
+int test__backward_ring_buffer(int subtest __maybe_unused)
+{
+        int ret = TEST_SKIP, err, sample_count = 0, comm_count = 0;
+        char pid[16], sbuf[STRERR_BUFSIZE];
+        struct perf_evlist *evlist;
+        struct perf_evsel *evsel __maybe_unused;
+        struct parse_events_error parse_error;
+        struct record_opts opts = {
+                .target = {
+                        .uid = UINT_MAX,
+                        .uses_mmap = true,
+                },
+                .freq         = 0,
+                .mmap_pages   = 256,
+                .default_interval = 1,
+        };
+
+        snprintf(pid, sizeof(pid), "%d", getpid());
+        pid[sizeof(pid) - 1] = '\0';
+        opts.target.tid = opts.target.pid = pid;
+
+        evlist = perf_evlist__new();
+        if (!evlist) {
+                pr_debug("No ehough memory to create evlist\n");
+                return TEST_FAIL;
+        }
+
+        err = perf_evlist__create_maps(evlist, &opts.target);
+        if (err < 0) {
+                pr_debug("Not enough memory to create thread/cpu maps\n");
+                goto out_delete_evlist;
+        }
+
+        bzero(&parse_error, sizeof(parse_error));
+        err = parse_events(evlist, "syscalls:sys_enter_prctl", &parse_error);
+        if (err) {
+                pr_debug("Failed to parse tracepoint event, try use root\n");
+                ret = TEST_SKIP;
+                goto out_delete_evlist;
+        }
+
+        perf_evlist__config(evlist, &opts, NULL);
+
+        /* Set backward bit, ring buffer should be writing from end */
+        evlist__for_each(evlist, evsel)
+                evsel->attr.write_backward = 1;
+
+        err = perf_evlist__open(evlist);
+        if (err < 0) {
+                pr_debug("perf_evlist__open: %s\n",
+                         strerror_r(errno, sbuf, sizeof(sbuf)));
+                goto out_delete_evlist;
+        }
+
+        ret = TEST_FAIL;
+        err = do_test(evlist, opts.mmap_pages, &sample_count,
+                      &comm_count);
+        if (err != TEST_OK)
+                goto out_delete_evlist;
+
+        if ((sample_count != NR_ITERS) || (comm_count != NR_ITERS)) {
+                pr_err("Unexpected counter: sample_count=%d, comm_count=%d\n",
+                       sample_count, comm_count);
+                goto out_delete_evlist;
+        }
+
+        err = do_test(evlist, 1, &sample_count, &comm_count);
+        if (err != TEST_OK)
+                goto out_delete_evlist;
+
+        ret = TEST_OK;
+out_delete_evlist:
+        perf_evlist__delete(evlist);
+        return ret;
+}
diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
index 93c467015e71..0e95c20ecf6e 100644
--- a/tools/perf/tests/builtin-test.c
+++ b/tools/perf/tests/builtin-test.c
@@ -208,6 +208,10 @@ static struct test generic_tests[] = {
                 .func = test__event_times,
         },
         {
+                .desc = "Test backward reading from ring buffer",
+                .func = test__backward_ring_buffer,
+        },
+        {
                 .func = NULL,
         },
 };
diff --git a/tools/perf/tests/tests.h b/tools/perf/tests/tests.h
index 0fc946989cf0..c57e72c826d2 100644
--- a/tools/perf/tests/tests.h
+++ b/tools/perf/tests/tests.h
@@ -86,6 +86,7 @@ int test__synthesize_stat(int subtest);
 int test__synthesize_stat_round(int subtest);
 int test__event_update(int subtest);
 int test__event_times(int subtest);
+int test__backward_ring_buffer(int subtest);
 
 #if defined(__arm__) || defined(__aarch64__)
 #ifdef HAVE_DWARF_UNWIND_SUPPORT