[patch] 02-use-o_direct-to-reduce-cache.patch

02-use-o_direct-to-reduce-cache.patch (text/plain), 2.54 KB, created by eroen on 2014-06-12 21:34:05 UTC

Use O_DIRECT to reduce cache effects.

From: eroen <[e-mail]>

Requires Linux 2.6 kernel and GNU userland.
---
 piozone.c |   33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/piozone.c b/piozone.c
index eaf32be..6f597b6 100644
--- a/piozone.c
+++ b/piozone.c
@@ -12,7 +12,14 @@
 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 */
 
+/* Compile with -D_GNU_SOURCE on compatible Linux systems to minimize */
+/* OS caching effects by using O_DIRECT for I/O. See open(2). */
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
 #include <stdio.h>
+#include <stdint.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <string.h>
@@ -31,7 +38,14 @@
 #define MB  ((uint64_t) 1000*KB)
 #define GB  ((uint64_t) 1000*MB)
 
-static char iobuf[1*MiB];
+#ifdef O_DIRECT
+#define ALIGNMENT 512
+#else
+#define ALIGNMENT 1
+#endif
+
+static char iobuf[1*MiB + ALIGNMENT - 1];
+static char *iobufalign;
 static volatile stopf = 0;
 static char *argv0 = "piozone";
 
@@ -75,12 +89,16 @@ bench_linear(int fd,
     int count = 0;
     int nr = 0;
     
+    if(debug)
+	printf("  off: %llx\n", off);
     lseek64(fd, off, SEEK_SET);
     signal(SIGALRM, sigalrm_handler);
     stopf = 0;
     printf("Testing... ");
+    if(debug)
+	printf("  iobufalign: %llx, len: %llx\n", iobufalign, len);
     alarm(ts);
-    while (!stopf && (nr = read(fd, iobuf, len)) == len)
+    while (!stopf && (nr = read(fd, iobufalign, len)) == len)
     {
 	print_dial();
 	++count;
@@ -124,7 +142,7 @@ bench_random(int fd,
     alarm(ts);
     while (!stopf &&
 	   lseek64(fd, off+((rand()&area)*MiB), SEEK_SET) != -1 &&
-	   (nr = read(fd, iobuf, len)) == len)
+	   (nr = read(fd, iobufalign, len)) == len)
     {
 	print_dial();
 	++count;
@@ -154,7 +172,6 @@ bench_random(int fd,
 uint64_t
 disksize(int fd)
 {
-    char buf[8*KiB];
     uint64_t off, del;
     
 
@@ -164,7 +181,7 @@ disksize(int fd)
     while (del > 8*KiB)
     {
 	if (lseek64(fd, off+del, SEEK_SET) < 0 \
-		|| read(fd, buf, 8*KiB) < 0)
+		|| read(fd, iobufalign, 8*KiB) < 0)
 	    del >>= 1;
 	else
 	    off += del;
@@ -193,6 +210,8 @@ main(int argc,
     int test_time = 30; /* seconds */
     int c;
 
+    iobufalign = (char*)((intptr_t)iobuf + (ALIGNMENT - 1) \
+	    & ~(intptr_t)(ALIGNMENT - 1));
 
     argv0 = argv[0];
 
@@ -233,7 +252,11 @@ main(int argc,
 	exit(1);
     }
 
+#ifdef O_DIRECT
+    fd = open(argv[optind], O_RDONLY|O_DIRECT);
+#else
     fd = open(argv[optind], O_RDONLY);
+#endif
     if (fd < 0)
     {
 	fprintf(stderr, "%s: %s: open failed: %s\n",