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Subject[PATCH] perf test x86: address multiplexing in rdpmc test
From
Counters may be being used for pinned or other events which inhibit the
instruction counter in the test from being scheduled - time_enabled > 0
but time_running == 0. This causes the test to fail with division by 0.
Add a sleep loop to ensure that the counter is run before computing
the count.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/arch/x86/tests/rdpmc.c | 45 ++++++++++++++++++++++++-------
1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/tools/perf/arch/x86/tests/rdpmc.c b/tools/perf/arch/x86/tests/rdpmc.c
index 1ea916656a2d..0b0792ae67f7 100644
--- a/tools/perf/arch/x86/tests/rdpmc.c
+++ b/tools/perf/arch/x86/tests/rdpmc.c
@@ -34,19 +34,35 @@ static u64 rdtsc(void)
return low | ((u64)high) << 32;
}

-static u64 mmap_read_self(void *addr)
+static u64 mmap_read_self(void *addr, bool *error)
{
struct perf_event_mmap_page *pc = addr;
- u32 seq, idx, time_mult = 0, time_shift = 0;
+ u32 seq, idx, time_mult = 0, time_shift = 0, sleep_count = 0;
u64 count, cyc = 0, time_offset = 0, enabled, running, delta;

+ *error = false;
do {
- seq = pc->lock;
- barrier();
-
- enabled = pc->time_enabled;
- running = pc->time_running;
-
+ do {
+ seq = pc->lock;
+ barrier();
+
+ enabled = pc->time_enabled;
+ running = pc->time_running;
+
+ if (running == 0) {
+ /*
+ * Event hasn't run, this may be caused by
+ * multiplexing.
+ */
+ sleep_count++;
+ if (sleep_count > 60) {
+ pr_err("Event failed to run. Are higher priority counters being sampled by a different process?\n");
+ *error = true;
+ return 0;
+ }
+ sleep(1);
+ }
+ } while (running == 0);
if (enabled != running) {
cyc = rdtsc();
time_mult = pc->time_mult;
@@ -131,13 +147,22 @@ static int __test__rdpmc(void)

for (n = 0; n < 6; n++) {
u64 stamp, now, delta;
+ bool error;

- stamp = mmap_read_self(addr);
+ stamp = mmap_read_self(addr, &error);
+ if (error) {
+ delta_sum = 0;
+ goto out_close;
+ }

for (i = 0; i < loops; i++)
tmp++;

- now = mmap_read_self(addr);
+ now = mmap_read_self(addr, &error);
+ if (error) {
+ delta_sum = 0;
+ goto out_close;
+ }
loops *= 10;

delta = now - stamp;
--
2.25.1.696.g5e7596f4ac-goog
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