[Libguestfs] [PATCH libnbd 1/7] common/utils: Add vector benchmarks

[Nir Soffer]

The generic vector reallocs on every append. Add benchmarks to measure
the cost with uint32 vector (used for copying extents) and the effect of
reserving space upfront.

The tests show that realloc is pretty efficient, but calling reserve
before the appends speeds the appends up significantly.

$ ./test-vector | grep bench
bench_reserve: 1000000 appends in 0.004159 s
bench_append: 1000000 appends in 0.014897 s

Signed-off-by: Nir Soffer <nsoffer at redhat.com>
---
 common/utils/Makefile.am   |  2 +-
 common/utils/bench.h       | 72 ++++++++++++++++++++++++++++++++++++++
 common/utils/test-vector.c | 49 ++++++++++++++++++++++++++
 3 files changed, 122 insertions(+), 1 deletion(-)
 create mode 100644 common/utils/bench.h

diff --git a/common/utils/Makefile.am b/common/utils/Makefile.am
index b273ada..4730cea 100644
--- a/common/utils/Makefile.am
+++ b/common/utils/Makefile.am
@@ -59,6 +59,6 @@ test_human_size_SOURCES = test-human-size.c human-size.c human-size.h
 test_human_size_CPPFLAGS = -I$(srcdir)
 test_human_size_CFLAGS = $(WARNINGS_CFLAGS)
 
-test_vector_SOURCES = test-vector.c vector.c vector.h
+test_vector_SOURCES = test-vector.c vector.c vector.h bench.h
 test_vector_CPPFLAGS = -I$(srcdir)
 test_vector_CFLAGS = $(WARNINGS_CFLAGS)
diff --git a/common/utils/bench.h b/common/utils/bench.h
new file mode 100644
index 0000000..496a361
--- /dev/null
+++ b/common/utils/bench.h
@@ -0,0 +1,72 @@
+/* libnbd
+ * Copyright (C) 2021 Red Hat Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Red Hat nor the names of its contributors may be
+ * used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+ * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef LIBNBD_BENCH_H
+#define LIBNBD_BENCH_H
+
+#include <sys/time.h>
+
+#define MICROSECONDS 1000000
+
+struct bench {
+    struct timeval start, stop;
+};
+
+static inline void
+bench_start(struct bench *b)
+{
+  gettimeofday (&b->start, NULL);
+}
+
+static inline void
+bench_stop(struct bench *b)
+{
+  gettimeofday (&b->stop, NULL);
+}
+
+static inline double
+bench_sec(struct bench *b)
+{
+  struct timeval dt;
+
+  dt.tv_sec = b->stop.tv_sec - b->start.tv_sec;
+  dt.tv_usec = b->stop.tv_usec - b->start.tv_usec;
+
+  if (dt.tv_usec < 0) {
+    dt.tv_sec -= 1;
+    dt.tv_usec += MICROSECONDS;
+  }
+
+  return ((double)dt.tv_sec * MICROSECONDS + dt.tv_usec) / MICROSECONDS;
+}
+
+#endif /* LIBNBD_BENCH_H */
diff --git a/common/utils/test-vector.c b/common/utils/test-vector.c
index 94b2aeb..28e882f 100644
--- a/common/utils/test-vector.c
+++ b/common/utils/test-vector.c
@@ -38,9 +38,13 @@
 #undef NDEBUG /* Keep test strong even for nbdkit built without assertions */
 #include <assert.h>
 
+#include "bench.h"
 #include "vector.h"
 
+#define APPENDS 1000000
+
 DEFINE_VECTOR_TYPE(int64_vector, int64_t);
+DEFINE_VECTOR_TYPE(uint32_vector, uint32_t);
 DEFINE_VECTOR_TYPE(string_vector, char *);
 
 static int
@@ -113,10 +117,55 @@ test_string_vector (void)
   free (v.ptr);
 }
 
+static void
+bench_reserve (void)
+{
+  uint32_vector v = empty_vector;
+  struct bench b;
+  int64_t usec;
+
+  bench_start(&b);
+
+  uint32_vector_reserve(&v, APPENDS);
+
+  for (uint32_t i = 0; i < APPENDS; i++) {
+    uint32_vector_append (&v, i);
+  }
+
+  bench_stop(&b);
+
+  assert (v.ptr[APPENDS - 1] == APPENDS - 1);
+  free (v.ptr);
+
+  printf ("bench_reserve: %d appends in %.6f s\n", APPENDS, bench_sec (&b));
+}
+
+static void
+bench_append (void)
+{
+  uint32_vector v = empty_vector;
+  struct bench b;
+
+  bench_start(&b);
+
+  for (uint32_t i = 0; i < APPENDS; i++) {
+    uint32_vector_append (&v, i);
+  }
+
+  bench_stop(&b);
+
+  assert (v.ptr[APPENDS - 1] == APPENDS - 1);
+  free (v.ptr);
+
+  printf ("bench_append: %d appends in %.6f s\n", APPENDS, bench_sec (&b));
+}
+
 int
 main (int argc, char *argv[])
 {
   test_int64_vector ();
   test_string_vector ();
+  bench_reserve ();
+  bench_append ();
   return 0;
 }
-- 
2.31.1