From a43c2b0bdfba2ad77d978f55130682c07d7fa6b3 Mon Sep 17 00:00:00 2001 From: Mark McLoughlin Date: Wed, 17 Jun 2009 11:38:28 +0100 Subject: [PATCH] virtio: add support for indirect ring entries Support 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: Anthony Liguori --- hw/virtio-pci.c | 4 +++- hw/virtio.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++----- hw/virtio.h | 4 ++++ 3 files changed, 53 insertions(+), 6 deletions(-) diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c index 24fe837..df45036 100644 --- a/hw/virtio-pci.c +++ b/hw/virtio-pci.c @@ -136,7 +136,9 @@ static uint32_t virtio_ioport_read(void *opaque, uint32_t addr) switch (addr) { case VIRTIO_PCI_HOST_FEATURES: ret = vdev->get_features(vdev); - ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY) | (1 << VIRTIO_F_BAD_FEATURE); + ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY); + ret |= (1 << VIRTIO_RING_F_INDIRECT_DESC); + ret |= (1 << VIRTIO_F_BAD_FEATURE); break; case VIRTIO_PCI_GUEST_FEATURES: ret = vdev->features; diff --git a/hw/virtio.c b/hw/virtio.c index 1e8376d..af71d99 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -293,18 +293,41 @@ static unsigned virtqueue_next_desc(target_phys_addr_t desc_pa, int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int out_bytes) { - target_phys_addr_t desc_pa = vq->vring.desc; - unsigned int idx, max; - int num_bufs, in_total, out_total; + unsigned int idx; + int total_bufs, in_total, out_total; idx = vq->last_avail_idx; - max = vq->vring.num; - num_bufs = in_total = out_total = 0; + total_bufs = in_total = out_total = 0; while (virtqueue_num_heads(vq, idx)) { + unsigned int max, num_bufs, indirect = 0; + target_phys_addr_t desc_pa; int i; + max = vq->vring.num; + num_bufs = total_bufs; i = virtqueue_get_head(vq, idx++); + desc_pa = vq->vring.desc; + + if (vring_desc_flags(desc_pa, i) & VRING_DESC_F_INDIRECT) { + if (vring_desc_len(desc_pa, i) % sizeof(VRingDesc)) { + fprintf(stderr, "Invalid size for indirect buffer table\n"); + exit(1); + } + + /* If we've got too many, that implies a descriptor loop. */ + if (num_bufs >= max) { + fprintf(stderr, "Looped descriptor"); + exit(1); + } + + /* loop over the indirect descriptor table */ + indirect = 1; + max = vring_desc_len(desc_pa, i) / sizeof(VRingDesc); + num_bufs = i = 0; + desc_pa = vring_desc_addr(desc_pa, i); + } + do { /* If we've got too many, that implies a descriptor loop. */ if (++num_bufs > max) { @@ -322,6 +345,11 @@ int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int out_bytes) return 1; } } while ((i = virtqueue_next_desc(desc_pa, i, max)) != max); + + if (!indirect) + total_bufs = num_bufs; + else + total_bufs++; } return 0; @@ -342,6 +370,19 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem) max = vq->vring.num; i = head = virtqueue_get_head(vq, vq->last_avail_idx++); + + if (vring_desc_flags(desc_pa, i) & VRING_DESC_F_INDIRECT) { + if (vring_desc_len(desc_pa, i) % sizeof(VRingDesc)) { + fprintf(stderr, "Invalid size for indirect buffer table\n"); + exit(1); + } + + /* loop over the indirect descriptor table */ + max = vring_desc_len(desc_pa, i) / sizeof(VRingDesc); + desc_pa = vring_desc_addr(desc_pa, i); + i = 0; + } + do { struct iovec *sg; int is_write = 0; diff --git a/hw/virtio.h b/hw/virtio.h index 425727e..46ed0b2 100644 --- a/hw/virtio.h +++ b/hw/virtio.h @@ -32,6 +32,8 @@ /* We notify when the ring is completely used, even if the guest is supressing * callbacks */ #define VIRTIO_F_NOTIFY_ON_EMPTY 24 +/* We support indirect buffer descriptors */ +#define VIRTIO_RING_F_INDIRECT_DESC 28 /* A guest should never accept this. It implies negotiation is broken. */ #define VIRTIO_F_BAD_FEATURE 30 @@ -41,6 +43,8 @@ #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 /* This means don't notify other side when buffer added. */ #define VRING_USED_F_NO_NOTIFY 1 -- 2.7.4