From 9fa29b9df32ba4db055f3977933cd0c1b8fe67cd Mon Sep 17 00:00:00 2001 From: Mark McLoughlin Date: Mon, 11 May 2009 18:11:45 +0100 Subject: virtio: indirect ring entries (VIRTIO_RING_F_INDIRECT_DESC) Add a new feature flag for indirect ring entries. These are ring entries which point to a table of buffer descriptors. The idea here is to increase the ring capacity by allowing a larger effective ring size whereby the ring size dictates the number of requests that may be outstanding, rather than the size of those requests. This should be most effective in the case of block I/O where we can potentially benefit by concurrently dispatching a large number of large requests. Even in the simple case of single segment block requests, this results in a threefold increase in ring capacity. Signed-off-by: Mark McLoughlin Signed-off-by: Rusty Russell --- include/linux/virtio_ring.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include') diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 166c519689d..693e0ec5afa 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -14,6 +14,8 @@ #define VRING_DESC_F_NEXT 1 /* This marks a buffer as write-only (otherwise read-only). */ #define VRING_DESC_F_WRITE 2 +/* This means the buffer contains a list of buffer descriptors. */ +#define VRING_DESC_F_INDIRECT 4 /* The Host uses this in used->flags to advise the Guest: don't kick me when * you add a buffer. It's unreliable, so it's simply an optimization. Guest @@ -24,6 +26,9 @@ * optimization. */ #define VRING_AVAIL_F_NO_INTERRUPT 1 +/* We support indirect buffer descriptors */ +#define VIRTIO_RING_F_INDIRECT_DESC 28 + /* Virtio ring descriptors: 16 bytes. These can chain together via "next". */ struct vring_desc { -- cgit v1.2.3