linux-kernel - [PATCH] perf test x86: address multiplexing in rdpmc test

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Message-Id: <20200321001400.245121-1-irogers@google.com>
Date:   Fri, 20 Mar 2020 17:14:00 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH] perf test x86: address multiplexing in rdpmc test

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@...gle.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