[LTP] [PATCH v3] fzsync: limit sampling time

[Jan Stancek]

Fixes: #429

Sampling can take considerably longer time on single CPU
and very slow systems. This patch limits sampling time to
1/2 of fuzzing runtime. If we don't have enough samples by
that time, stop sampling and use stats we gathered so far.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
 include/tst_fuzzy_sync.h | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

Changes in v3:
- base sampling time directly on exec time

diff --git a/include/tst_fuzzy_sync.h b/include/tst_fuzzy_sync.h
index 03f69b78bc82..18b9d265bbb4 100644
--- a/include/tst_fuzzy_sync.h
+++ b/include/tst_fuzzy_sync.h
@@ -70,6 +70,9 @@
 #ifndef TST_FUZZY_SYNC_H__
 #define TST_FUZZY_SYNC_H__
 
+/* how much of exec time is sampling allowed to take */
+#define SAMPLING_SLICE 0.5f
+
 /** Some statistics for a variable */
 struct tst_fzsync_stat {
 	float avg;
@@ -582,17 +585,21 @@ static inline void tst_fzsync_wait_b(struct tst_fzsync_pair *pair)
 static inline int tst_fzsync_run_a(struct tst_fzsync_pair *pair)
 {
 	int exit = 0;
+	float rem_p = 1 - tst_timeout_remaining() / pair->exec_time_start;
+
+	/* Limit amount of time spent on sampling */
+	if ((pair->exec_time_p * SAMPLING_SLICE < rem_p)
+		&& (pair->sampling > 0)) {
+		tst_res(TINFO, "stopping sampling at %d samples",
+			pair->exec_loop);
+		pair->sampling = 0;
+		tst_fzsync_pair_info(pair);
+	}
 
-	if (pair->exec_time_p
-	    < 1 - tst_timeout_remaining() / pair->exec_time_start) {
+	if (pair->exec_time_p < rem_p) {
 		tst_res(TINFO,
 			"Exceeded execution time, requesting exit");
 		exit = 1;
-
-		if (pair->sampling > 0) {
-			tst_res(TWARN,
-				"Still sampling, consider increasing LTP_TIMEOUT_MUL");
-		}
 	}
 
 	if (++pair->exec_loop > pair->exec_loops) {
-- 
1.8.3.1