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From: Aurelien Jarno <aurelien@aurel32.net>
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Date: Sun, 30 Nov 2008 19:12:50 +0000
Subject: [Qemu-devel] [5839] qemu-img: open files with cache=writeback
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Revision: 5839
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5839
Author:   aurel32
Date:     2008-11-30 19:12:49 +0000 (Sun, 30 Nov 2008)

Log Message:
-----------
qemu-img: open files with cache=writeback

Data integrity is not important in qemu-img, so open the files with
cache=writeback. This fixes the performance regression seen with qemu-img
since revision 5485, and most particularly with the qcow2 format.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

Revision Links:
--------------
    http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5485

Modified Paths:
--------------
    trunk/qemu-img.c

Modified: trunk/qemu-img.c
===================================================================
--- trunk/qemu-img.c	2008-11-30 17:54:28 UTC (rev 5838)
+++ trunk/qemu-img.c	2008-11-30 19:12:49 UTC (rev 5839)
@@ -30,6 +30,9 @@
 #include <windows.h>
 #endif
 
+/* Default to cache=writeback as data integrity is not important for qemu-tcg. */
+#define BRDV_O_FLAGS BDRV_O_CACHE_WB
+
 static void __attribute__((noreturn)) error(const char *fmt, ...)
 {
     va_list ap;
@@ -186,7 +189,7 @@
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, 0, drv) < 0) {
+    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     if (bdrv_is_encrypted(bs)) {
@@ -317,7 +320,7 @@
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, 0, drv) < 0) {
+    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     ret = bdrv_commit(bs);
@@ -691,7 +694,7 @@
     } else {
         drv = NULL;
     }
-    if (bdrv_open2(bs, filename, 0, drv) < 0) {
+    if (bdrv_open2(bs, filename, BRDV_O_FLAGS, drv) < 0) {
         error("Could not open '%s'", filename);
     }
     bdrv_get_format(bs, fmt_name, sizeof(fmt_name));