From 78ca5558451e29a6245f7a75c9b454a6ce7012f3 Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Thu, 10 Nov 2011 21:11:19 +0100
Subject: [PATCH] bench: optimize io.c benchmark

Use static buffers. Most clock ticks were spent in malloc() and free() instead
of read() and write().

Fix measurements. Really fast runs would result in bogus results like:

  Wrote 1048576000 bytes in -0.731630s using 8192 byte buffers: -1366.811093mB/s
---
 benchmark/io.c | 65 ++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 38 insertions(+), 27 deletions(-)

diff --git a/benchmark/io.c b/benchmark/io.c
index db3f04c..53a5231 100644
--- a/benchmark/io.c
+++ b/benchmark/io.c
@@ -2,41 +2,47 @@
  * gcc -o iotest io.c
  */
 
+#include <assert.h>
 #include <unistd.h>
 #include <string.h>
 #include <fcntl.h>
 #include <sys/time.h>
 #include <assert.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <stdio.h>
  
-int tsize = 1000 * 1048576;
-const char *path = "/tmp/wt.dat";
+static int c = 0;
+static int tsize = 1000 * 1048576;
+static const char path[] = "/tmp/wt.dat";
+static char buf[65536];
 
-int c = 0;
+static uint64_t now(void) {
+  struct timeval tv;
 
-char* bufit(size_t l)
-{
-  char *p = malloc(l);
-  memset(p, '!', l);
-  return p;
+  if (gettimeofday(&tv, NULL))
+    abort();
+
+  return tv.tv_sec * 1000000ULL + tv.tv_usec;
 }
 
-void writetest(int size, size_t bsize)
+static void writetest(int size, size_t bsize)
 {
   int i;
-  char *buf = bufit(bsize);
-  struct timeval start, end;
+  uint64_t start, end;
   double elapsed;
   double mbps;
 
+  assert(bsize <= sizeof buf);
+
   int fd = open(path, O_CREAT|O_WRONLY, 0644);
   if (fd < 0) {
     perror("open failed");
     exit(254);
   }
 
-  assert(0 ==  gettimeofday(&start, NULL));
+  start = now();
+
   for (i = 0; i < size; i += bsize) {
     int rv = write(fd, buf, bsize);
     if (c++ % 2000 == 0) fprintf(stderr, ".");
@@ -45,35 +51,40 @@ void writetest(int size, size_t bsize)
       exit(254);
     }
   }
-#ifdef __linux__
+  close(fd);
+
+#ifndef NSYNC
+# ifdef __linux__
   fdatasync(fd);
-#else
+# else
   fsync(fd);
-#endif
-  close(fd);
-  assert(0 == gettimeofday(&end, NULL));
-  elapsed = (end.tv_sec - start.tv_sec) + ((double)(end.tv_usec - start.tv_usec))/100000.;
+# endif
+#endif /* SYNC */
+
+  end = now();
+  elapsed = (end - start) / 1e6;
   mbps = ((tsize/elapsed)) / 1048576;
-  fprintf(stderr, "\nWrote %d bytes in %03fs using %ld byte buffers: %03fmB/s\n", size, elapsed, bsize, mbps);
 
-  free(buf);
+  fprintf(stderr, "\nWrote %d bytes in %03fs using %ld byte buffers: %03fmB/s\n", size, elapsed, bsize, mbps);
 }
 
 void readtest(int size, size_t bsize)
 {
   int i;
-  char *buf = bufit(bsize);
-  struct timeval start, end;
+  uint64_t start, end;
   double elapsed;
   double mbps;
 
+  assert(bsize <= sizeof buf);
+
   int fd = open(path, O_RDONLY, 0644);
   if (fd < 0) {
     perror("open failed");
     exit(254);
   }
 
-  assert(0 == gettimeofday(&start, NULL));
+  start = now();
+
   for (i = 0; i < size; i += bsize) {
     int rv = read(fd, buf, bsize);
     if (rv < 0) {
@@ -82,12 +93,12 @@ void readtest(int size, size_t bsize)
     }
   }
   close(fd);
-  assert(0 == gettimeofday(&end, NULL));
-  elapsed = (end.tv_sec - start.tv_sec) + ((double)(end.tv_usec - start.tv_usec))/100000.;
+
+  end = now();
+  elapsed = (end - start) / 1e6;
   mbps = ((tsize/elapsed)) / 1048576;
-  fprintf(stderr, "Read %d bytes in %03fs using %ld byte buffers: %03fmB/s\n", size, elapsed, bsize, mbps);
 
-  free(buf);
+  fprintf(stderr, "Read %d bytes in %03fs using %ld byte buffers: %03fmB/s\n", size, elapsed, bsize, mbps);
 }
 
 void cleanup() {
-- 
2.7.4