[PATCH V3 12/12] perf top: check the latency of perf_top__mmap_read

[kan . liang]

From: Kan Liang <kan.li...@intel.com>

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.li...@intel.com>
---
 tools/perf/builtin-top.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 3c14333..8fb007b 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -877,8 +877,10 @@ 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);
 
@@ -889,6 +891,13 @@ 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");
 }
 
 /*
-- 
2.5.5