In the case of using indirect, indirect desc must be allocated and
released each time, which increases a lot of cpu overhead.
Here, a cache is added for indirect. If the number of indirect desc to be
applied for is less than desc_cache_thr, the desc array with
the size of desc_cache_thr is fixed and cached for reuse.
Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 126 ++++++++++++++++++++++++++++++++---
include/linux/virtio.h | 17 +++++
2 files changed, 135 insertions(+), 8 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index dd95dfd85e98..a4a91c497a83 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -85,6 +85,19 @@ struct vring_desc_extra {
u16 next; /* The next desc state in a list. */
};
+struct vring_desc_cache {
+ /* desc cache chain */
+ struct list_head list;
+
+ void *array;
+
+ /* desc cache threshold
+ * 0 - disable desc cache
+ * > 0 - enable desc cache. As the threshold of the desc cache.
+ */
+ u32 threshold;
+};
+
struct vring_virtqueue {
struct virtqueue vq;
@@ -117,6 +130,8 @@ struct vring_virtqueue {
/* Hint for event idx: already triggered no need to disable. */
bool event_triggered;
+ struct vring_desc_cache desc_cache;
+
union {
/* Available for split ring */
struct {
@@ -423,7 +438,50 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
return extra[i].next;
}
-static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
+static void desc_cache_init(struct vring_virtqueue *vq)
+{
+ vq->desc_cache.array = NULL;
+ vq->desc_cache.threshold = 0;
+ INIT_LIST_HEAD(&vq->desc_cache.list);
+}
+
+static void desc_cache_free(struct vring_virtqueue *vq)
+{
+ kfree(vq->desc_cache.array);
+}
+
+static void __desc_cache_put(struct vring_virtqueue *vq,
+ struct list_head *node, int n)
+{
+ if (n <= vq->desc_cache.threshold)
+ list_add(node, &vq->desc_cache.list);
+ else
+ kfree(node);
+}
+
+#define desc_cache_put(vq, desc, n) \
+ __desc_cache_put(vq, (struct list_head *)desc, n)
+
+static void *desc_cache_get(struct vring_virtqueue *vq,
+ int size, int n, gfp_t gfp)
+{
+ struct list_head *node;
+
+ if (n > vq->desc_cache.threshold)
+ return kmalloc_array(n, size, gfp);
+
+ node = vq->desc_cache.list.next;
+ list_del(node);
+ return node;
+}
+
+#define _desc_cache_get(vq, n, gfp, tp) \
+ ((tp *)desc_cache_get(vq, (sizeof(tp)), n, gfp))
+
+#define desc_cache_get_split(vq, n, gfp) \
+ _desc_cache_get(vq, n, gfp, struct vring_desc)
+
+static struct vring_desc *alloc_indirect_split(struct vring_virtqueue *vq,
unsigned int total_sg,
gfp_t gfp)
{
@@ -437,12 +495,12 @@ static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
*/
gfp &= ~__GFP_HIGHMEM;
- desc = kmalloc_array(total_sg, sizeof(struct vring_desc), gfp);
+ desc = desc_cache_get_split(vq, total_sg, gfp);
if (!desc)
return NULL;
for (i = 0; i < total_sg; i++)
- desc[i].next = cpu_to_virtio16(_vq->vdev, i + 1);
+ desc[i].next = cpu_to_virtio16(vq->vq.vdev, i + 1);
return desc;
}
@@ -508,7 +566,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
head = vq->free_head;
if (virtqueue_use_indirect(_vq, total_sg))
- desc = alloc_indirect_split(_vq, total_sg, gfp);
+ desc = alloc_indirect_split(vq, total_sg, gfp);
else {
desc = NULL;
WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
@@ -652,7 +710,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
}
if (indirect)
- kfree(desc);
+ desc_cache_put(vq, desc, total_sg);
END_USE(vq);
return -ENOMEM;
@@ -717,7 +775,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
if (vq->indirect) {
struct vring_desc *indir_desc =
vq->split.desc_state[head].indir_desc;
- u32 len;
+ u32 len, n;
/* Free the indirect table, if any, now that it's unmapped. */
if (!indir_desc)
@@ -729,10 +787,12 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
VRING_DESC_F_INDIRECT));
BUG_ON(len == 0 || len % sizeof(struct vring_desc));
- for (j = 0; j < len / sizeof(struct vring_desc); j++)
+ n = len / sizeof(struct vring_desc);
+
+ for (j = 0; j < n; j++)
vring_unmap_one_split_indirect(vq, &indir_desc[j]);
- kfree(indir_desc);
+ desc_cache_put(vq, indir_desc, n);
vq->split.desc_state[head].indir_desc = NULL;
} else if (ctx) {
*ctx = vq->split.desc_state[head].indir_desc;
@@ -2200,6 +2260,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
!context;
vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
+ desc_cache_init(vq);
+
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
@@ -2329,6 +2391,7 @@ void vring_del_virtqueue(struct virtqueue *_vq)
if (!vq->packed_ring) {
kfree(vq->split.desc_state);
kfree(vq->split.desc_extra);
+ desc_cache_free(vq);
}
kfree(vq);
}
@@ -2445,6 +2508,53 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);
+int virtqueue_set_desc_cache(struct virtqueue *_vq, u32 threshold)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ struct list_head *node;
+ int size, num, i;
+
+ BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_desc));
+ BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_packed_desc));
+
+ BUG_ON(!vq->we_own_ring);
+
+ if (!vq->indirect)
+ return 0;
+
+ vq->desc_cache.threshold = threshold;
+
+ if (!threshold)
+ return 0;
+
+ if (vq->packed_ring) {
+ size = sizeof(struct vring_packed_desc);
+ num = vq->packed.vring.num;
+ } else {
+ size = sizeof(struct vring_desc);
+ num = vq->split.vring.num;
+ }
+
+ size = size * vq->desc_cache.threshold;
+
+ vq->desc_cache.array = kmalloc_array(num, size, GFP_KERNEL);
+ if (!vq->desc_cache.array) {
+ vq->desc_cache.threshold = 0;
+ dev_warn(&vq->vq.vdev->dev,
+ "queue[%d] alloc desc cache fail. turn off it.\n",
+ vq->vq.index);
+ return -1;
+ }
+
+ for (i = 0; i < num; ++i) {
+ node = vq->desc_cache.array + (i * size);
+ list_add(node, &vq->desc_cache.list);
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(virtqueue_set_desc_cache);
+
/* Only available for split ring */
const struct vring *virtqueue_get_vring(struct virtqueue *vq)
{
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 41edbc01ffa4..e24b2e90dd42 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -89,6 +89,23 @@ dma_addr_t virtqueue_get_desc_addr(struct virtqueue *vq);
dma_addr_t virtqueue_get_avail_addr(struct virtqueue *vq);
dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq);
+/**
+ * virtqueue_set_desc_cache - set virtio ring desc cache threshold
+ *
+ * virtio will allocate ring.num desc arrays of size threshold in advance. If
+ * total_sg exceeds the threshold, use kmalloc/kfree allocation indirect desc,
+ * if total_sg is less than or equal to the threshold, use these pre-allocated
+ * desc arrays.
+ *
+ * This function must be called immediately after find_vqs and before device
+ * ready.
+ *
+ * @threshold:
+ * 0 - disable desc cache
+ * > 0 - enable desc cache. As the threshold of the desc cache.
+ */
+int virtqueue_set_desc_cache(struct virtqueue *_vq, u32 threshold);
+
/**
* virtio_device - representation of a device using virtio
* @index: unique position on the virtio bus
--
2.31.0
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
