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Subject[PATCH V4 11/15] perf top: add overwrite fall back
Date
From: Kan Liang <kan.liang@intel.com>

Switch to non-overwrite mode if kernel doesnot support overwrite
ringbuffer.

It's only effect when overwrite mode is supported.
No change to current behavior.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
tools/perf/builtin-top.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index c86eee4..ecba2cd 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -943,6 +943,27 @@ static int perf_top_overwrite_check(struct perf_top *top)
return 0;
}

+static int perf_top_overwrite_fallback(struct perf_top *top,
+ struct perf_evsel *evsel)
+{
+ struct record_opts *opts = &top->record_opts;
+ struct perf_evlist *evlist = top->evlist;
+ struct perf_evsel *counter;
+
+ if (!opts->overwrite)
+ return 0;
+
+ /* only fall back when first event fails */
+ if (evsel != perf_evlist__first(evlist))
+ return 0;
+
+ evlist__for_each_entry(evlist, counter)
+ counter->attr.write_backward = false;
+ opts->overwrite = false;
+ ui__warning("fall back to non-overwrite mode\n");
+ return 1;
+}
+
static int perf_top__start_counters(struct perf_top *top)
{
char msg[BUFSIZ];
@@ -967,6 +988,21 @@ static int perf_top__start_counters(struct perf_top *top)
try_again:
if (perf_evsel__open(counter, top->evlist->cpus,
top->evlist->threads) < 0) {
+
+ /*
+ * Specially handle overwrite fall back.
+ * Because perf top is the only tool which has
+ * overwrite mode by default, support
+ * both overwrite and non-overwrite mode, and
+ * require consistent mode for all events.
+ *
+ * May move it to generic code with more tools
+ * have similar attribute.
+ */
+ if (is_write_backward_fail() &&
+ perf_top_overwrite_fallback(top, counter))
+ goto try_again;
+
if (perf_evsel__fallback(counter, errno, msg, sizeof(msg))) {
if (verbose > 0)
ui__warning("%s\n", msg);
--
2.5.5
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