perf top: Check the latency of perf_top__mmap_read()

The latency of perf_top__mmap_read() should be lower than refresh time.
If not, give some hints to reduce the latency.

Signed-off-by: Kan Liang <kan.liang@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1516310792-208685-18-git-send-email-kan.liang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 2b4914f34ed6a52a94b8b6fa8cbd8af4ec7eacea..b7c823ba8374fb702b4ae3d3033e79b852e4686b 100644 (file)
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -889,8 +889,10 @@ static void perf_top__mmap_read(struct perf_top *top)
 {
        bool overwrite = top->record_opts.overwrite;
        struct perf_evlist *evlist = top->evlist;
+       unsigned long long start, end;
        int i;
 
+       start = rdclock();
        if (overwrite)
                perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_DATA_PENDING);
 
@@ -901,6 +903,13 @@ static void perf_top__mmap_read(struct perf_top *top)
                perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_EMPTY);
                perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
        }
+       end = rdclock();
+
+       if ((end - start) > (unsigned long long)top->delay_secs * NSEC_PER_SEC)
+               ui__warning("Too slow to read ring buffer.\n"
+                           "Please try increasing the period (-c) or\n"
+                           "decreasing the freq (-F) or\n"
+                           "limiting the number of CPUs (-C)\n");
 }
 
 /*