qemu: improve scsi dma speed by increasing the dma buffer size

taken from Xen 17267:f4a92f0db20f, original patch by Samuel Thibault.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5385 c046a42c-6fe2-441c-8c8c-71466251a162

hw/scsi-disk.c

@@ -34,7 +34,7 @@ do { fprintf(stderr, "scsi-disk: " fmt , ##args); } while (0)
 #define SENSE_HARDWARE_ERROR  4
 #define SENSE_ILLEGAL_REQUEST 5
 
-#define SCSI_DMA_BUF_SIZE    65536
+#define SCSI_DMA_BUF_SIZE    131072
 
 typedef struct SCSIRequest {
     SCSIDeviceState *dev;