UBUNTU: SAUCE: Improve Amazon EBS performance for EC2

OriginalAuthor: Amazona from Ben Howard <behoward@amazon.com>
BugLink: http://bugs.launchpad.net/bugs/634316

The pv-ops kernel suffers from poor performance when using Amazon's
Elastic block storage (EBS).  This patch from Amazon improves pv-ops
kernel performance, and has not exhibited any regressions.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index 3d5d6db864f..db03ee9eac4 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -106,6 +106,18 @@ struct blkif_response {
 
 DEFINE_RING_TYPES(blkif, struct blkif_request, struct blkif_response);
 
+/*
+ * Maximum number of pages used for a blkif ring
+ * max-ring-pages advertised by blkback to blkfront may be lowered at blkback
+ * mod load time.   Load time param set to default.
+ */
+#define BLKIF_MAX_NUM_RING_PAGES 16
+#define BLKIF_MAX_NUM_RING_PAGES_DFLT 4
+#if BLKIF_MAX_NUM_RING_PAGES < BLKIF_MAX_NUM_RING_PAGES_DFLT
+#undef BLKIF_MAX_NUM_RING_PAGES_DFLT
+#define BLKIF_MAX_NUM_RING_PAGES_DFLT BLKIF_MAX_NUM_RING_PAGES
+#endif
+
 #define VDISK_CDROM        0x1
 #define VDISK_REMOVABLE    0x2
 #define VDISK_READONLY     0x4