bcachefs: time stats now shows standard deviation.

Signed-off-by: Daniel Hill <daniel@gluo.nz>

6 files changed, 90 insertions, 7 deletions

diff --git a/fs/bcachefs/Kconfig b/fs/bcachefs/Kconfig
index 008886967841..cc3816ccca19 100644
--- a/fs/bcachefs/Kconfig
+++ b/fs/bcachefs/Kconfig
@@ -57,3 +57,8 @@ config BCACHEFS_LOCK_TIME_STATS
        depends on BCACHEFS_FS
        help
        Expose statistics for how long we held a lock in debugfs
+
+config BCACHEFS_UNIT_TESTS
+       tristate "bcachefs kunit tests" if !KUNIT_ALL_TESTS
+       depends on BCACHEFS_FS && KUNIT
+       default KUNIT_ALL_TESTS
diff --git a/fs/bcachefs/Makefile b/fs/bcachefs/Makefile
index 5dad8ed03a20..a54f58bd273f 100644
--- a/fs/bcachefs/Makefile
+++ b/fs/bcachefs/Makefile
@@ -67,3 +67,5 @@ bcachefs-y		:=	\
 	xattr.o
 
 bcachefs-$(CONFIG_BCACHEFS_POSIX_ACL) += acl.o
+
+obj-$(CONFIG_BCACHEFS_UNIT_TESTS) += unit_tests.o
diff --git a/fs/bcachefs/unit_tests.c b/fs/bcachefs/unit_tests.c
new file mode 100644
index 000000000000..59490bab2e7f
--- /dev/null
+++ b/fs/bcachefs/unit_tests.c
@@ -0,0 +1,48 @@
+#include <kunit/test.h>
+#include "util.h"
+
+static void util_test_basic(struct kunit *test)
+{
+    u64 mean = 0;
+    u64 var  = 0;
+    u64 i;
+    u64 val;
+
+    for ( i = 100 ; i <= 540 ; i += 20 ) {
+	    ewma_cal(&mean, &var, 8, i);
+    }
+    val = 119;
+    KUNIT_EXPECT_GE(test, mean, val - val / 10);
+    KUNIT_EXPECT_LE(test, mean, val + val / 10);
+
+    val = 5442;
+    KUNIT_EXPECT_GE(test, var, val - val / 10);
+    KUNIT_EXPECT_LE(test, var, val + val / 10);
+
+    mean = 0;
+    var  = 0;
+
+    for ( i = 1000 ; i <= 5400 ; i += 200 ) {
+	    ewma_cal(&mean, &var, 8, i);
+    }
+    val = 1192;
+    KUNIT_EXPECT_GE(test, mean, val - val / 100);
+    KUNIT_EXPECT_LE(test, mean, val + val / 100);
+
+    val = 544257;
+    KUNIT_EXPECT_GE(test, var, val - val / 100);
+    KUNIT_EXPECT_LE(test, var, val + val / 100);
+
+}
+
+static struct kunit_case util_test_cases[] = {
+	KUNIT_CASE(util_test_basic),
+	{}
+};
+
+static struct kunit_suite util_test_suite = {
+.name = "util test cases",
+.test_cases = util_test_cases
+};
+
+kunit_test_suite(util_test_suite);
diff --git a/fs/bcachefs/unit_tests.h b/fs/bcachefs/unit_tests.h
new file mode 100644
index 000000000000..59111ba18768
--- /dev/null
+++ b/fs/bcachefs/unit_tests.h
@@ -0,0 +1,6 @@
+#ifndef UNIT_TESTS_H_
+#define UNIT_TESTS_H_
+
+
+
+#endif // UNIT_TESTS_H_
diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c
index 42da6623d815..533da82b935e 100644
--- a/fs/bcachefs/util.c
+++ b/fs/bcachefs/util.c
@@ -288,13 +288,12 @@ static void bch2_time_stats_update_one(struct time_stats *stats,
 
 	stats->count++;
 
-	stats->average_duration = stats->average_duration
-		? ewma_add(stats->average_duration, duration, 6)
-		: duration;
-
-	stats->average_frequency = stats->average_frequency
-		? ewma_add(stats->average_frequency, freq, 6)
-		: freq;
+	ewma_cal(&stats->average_duration,
+		 &stats->variance_duration,
+		 8, duration);
+	ewma_cal(&stats->average_frequency,
+		 NULL,
+		 8, freq);
 
 	stats->max_duration = max(stats->max_duration, duration);
 
@@ -397,6 +396,10 @@ void bch2_time_stats_to_text(struct printbuf *out, struct time_stats *stats)
 	pr_time_units(out, stats->average_duration);
 
 	prt_newline(out);
+	prt_printf(out, "stddev duration:\t");
+	pr_time_units(out, int_sqrt64(stats->variance_duration));
+
+	prt_newline(out);
 	prt_printf(out, "max duration:\t");
 	pr_time_units(out, stats->max_duration);
 
diff --git a/fs/bcachefs/util.h b/fs/bcachefs/util.h
index ab7e43d4bf8b..88619f06b437 100644
--- a/fs/bcachefs/util.h
+++ b/fs/bcachefs/util.h
@@ -381,6 +381,7 @@ struct time_stats {
 	/* all fields are in nanoseconds */
 	u64		average_duration;
 	u64		average_frequency;
+	u64		variance_duration;
 	u64		max_duration;
 	u64		last_event;
 	struct quantiles quantiles;
@@ -408,6 +409,24 @@ void bch2_time_stats_init(struct time_stats *);
 	(((_ewma << _weight) - _ewma) + (val)) >> _weight;		\
 })
 
+static inline void ewma_cal(u64 *_mean, u64 *_variance, u64 weight, u64 val)
+{
+	u64 m = *_mean;
+	u64 v = *_variance;
+	s64 d = val - m;
+	u64 d2 = d*d;
+
+	if (m) {
+		*_mean = ((m << weight) + d) >> weight;
+		if (_variance)
+			*_variance = (((1 << weight) - 1) * ( (v << weight) + d2)) >> (weight + weight);
+	} else {
+		*_mean = val;
+		if (_variance)
+			*_variance = 0;
+	}
+}
+
 struct bch_ratelimit {
 	/* Next time we want to do some work, in nanoseconds */
 	u64			next;