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Date: Wed, 27 Oct 2021 14:19:11 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH 1/3] virtio: cache indirect desc for split
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 VIRT_QUEUE_CACHE_DESC_NUM, the desc array with
the size of VIRT_QUEUE_CACHE_DESC_NUM is fixed and cached for reuse.
Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
---
drivers/virtio/virtio.c | 6 ++++
drivers/virtio/virtio_ring.c | 63 ++++++++++++++++++++++++++++++------
include/linux/virtio.h | 10 ++++++
3 files changed, 70 insertions(+), 9 deletions(-)
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 0a5b54034d4b..04bcb74e5b9a 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -431,6 +431,12 @@ bool is_virtio_device(struct device *dev)
}
EXPORT_SYMBOL_GPL(is_virtio_device);
+void virtio_use_desc_cache(struct virtio_device *dev, bool val)
+{
+ dev->desc_cache = val;
+}
+EXPORT_SYMBOL_GPL(virtio_use_desc_cache);
+
void unregister_virtio_device(struct virtio_device *dev)
{
int index = dev->index; /* save for after device release */
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index dd95dfd85e98..0b9a8544b0e8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -117,6 +117,10 @@ struct vring_virtqueue {
/* Hint for event idx: already triggered no need to disable. */
bool event_triggered;
+ /* Is indirect cache used? */
+ bool use_desc_cache;
+ void *desc_cache_chain;
+
union {
/* Available for split ring */
struct {
@@ -423,12 +427,47 @@ 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,
+#define VIRT_QUEUE_CACHE_DESC_NUM 4
+
+static void desc_cache_chain_free_split(void *chain)
+{
+ struct vring_desc *desc;
+
+ while (chain) {
+ desc = chain;
+ chain = (void *)desc->addr;
+ kfree(desc);
+ }
+}
+
+static void desc_cache_put_split(struct vring_virtqueue *vq,
+ struct vring_desc *desc, int n)
+{
+ if (vq->use_desc_cache && n <= VIRT_QUEUE_CACHE_DESC_NUM) {
+ desc->addr = (u64)vq->desc_cache_chain;
+ vq->desc_cache_chain = desc;
+ } else {
+ kfree(desc);
+ }
+}
+
+static struct vring_desc *alloc_indirect_split(struct vring_virtqueue *vq,
unsigned int total_sg,
gfp_t gfp)
{
struct vring_desc *desc;
- unsigned int i;
+ unsigned int i, n;
+
+ if (vq->use_desc_cache && total_sg <= VIRT_QUEUE_CACHE_DESC_NUM) {
+ if (vq->desc_cache_chain) {
+ desc = vq->desc_cache_chain;
+ vq->desc_cache_chain = (void *)desc->addr;
+ goto got;
+ }
+ n = VIRT_QUEUE_CACHE_DESC_NUM;
+ } else {
+ n = total_sg;
+ }
/*
* We require lowmem mappings for the descriptors because
@@ -437,12 +476,13 @@ static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
*/
gfp &= ~__GFP_HIGHMEM;
- desc = kmalloc_array(total_sg, sizeof(struct vring_desc), gfp);
+ desc = kmalloc_array(n, sizeof(struct vring_desc), gfp);
if (!desc)
return NULL;
+got:
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 +548,7 @@ 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 +692,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
}
if (indirect)
- kfree(desc);
+ desc_cache_put_split(vq, desc, total_sg);
END_USE(vq);
return -ENOMEM;
@@ -717,7 +757,7 @@ 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 +769,12 @@ 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_split(vq, indir_desc, n);
vq->split.desc_state[head].indir_desc = NULL;
} else if (ctx) {
*ctx = vq->split.desc_state[head].indir_desc;
@@ -2199,6 +2241,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
!context;
vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
+ vq->desc_cache_chain = NULL;
+ vq->use_desc_cache = vdev->desc_cache;
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
@@ -2329,6 +2373,7 @@ void vring_del_virtqueue(struct virtqueue *_vq)
if (!vq->packed_ring) {
kfree(vq->split.desc_state);
kfree(vq->split.desc_extra);
+ desc_cache_chain_free_split(vq->desc_cache_chain);
}
kfree(vq);
}
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 41edbc01ffa4..d84b7b8f4070 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -109,6 +109,7 @@ struct virtio_device {
bool failed;
bool config_enabled;
bool config_change_pending;
+ bool desc_cache;
spinlock_t config_lock;
spinlock_t vqs_list_lock; /* Protects VQs list access */
struct device dev;
@@ -130,6 +131,15 @@ int register_virtio_device(struct virtio_device *dev);
void unregister_virtio_device(struct virtio_device *dev);
bool is_virtio_device(struct device *dev);
+/**
+ * virtio_use_desc_cache - virtio ring use desc cache
+ *
+ * virtio will cache the allocated indirect desc.
+ *
+ * This function must be called before find_vqs.
+ */
+void virtio_use_desc_cache(struct virtio_device *dev, bool val);
+
void virtio_break_device(struct virtio_device *dev);
void virtio_config_changed(struct virtio_device *dev);
--
2.31.0
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