If the VIRTIO_RING_F_INDIRECT_DESC negotiation succeeds, and the number of sgs used for sending packets is greater than 1. We must constantly call __kmalloc/kfree to allocate/release desc. In the case of extremely fast package delivery, the overhead cannot be ignored: 27.46% [kernel] [k] virtqueue_add 16.66% [kernel] [k] detach_buf_split 16.51% [kernel] [k] virtnet_xsk_xmit 14.04% [kernel] [k] virtqueue_add_outbuf 5.18% [kernel] [k] __kmalloc 4.08% [kernel] [k] kfree 2.80% [kernel] [k] virtqueue_get_buf_ctx 2.22% [kernel] [k] xsk_tx_peek_desc 2.08% [kernel] [k] memset_erms 0.83% [kernel] [k] virtqueue_kick_prepare 0.76% [kernel] [k] virtnet_xsk_run 0.62% [kernel] [k] __free_old_xmit_ptr 0.60% [kernel] [k] vring_map_one_sg 0.53% [kernel] [k] native_apic_mem_write 0.46% [kernel] [k] sg_next 0.43% [kernel] [k] sg_init_table 0.41% [kernel] [k] kmalloc_slab This patch adds a cache function to virtio to cache these allocated indirect desc instead of constantly allocating and releasing desc. v2: use struct list_head to cache the desc Xuan Zhuo (3): virtio: cache indirect desc for split virtio: cache indirect desc for packed virtio-net: enable virtio indirect cache drivers/net/virtio_net.c | 12 ++++ drivers/virtio/virtio.c | 6 ++ drivers/virtio/virtio_ring.c | 104 +++++++++++++++++++++++++++++------ include/linux/virtio.h | 14 +++++ 4 files changed, 119 insertions(+), 17 deletions(-) -- 2.31.0
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 at linux.alibaba.com>
---
drivers/virtio/virtio.c | 6 +++
drivers/virtio/virtio_ring.c | 77 ++++++++++++++++++++++++++++++++----
include/linux/virtio.h | 14 +++++++
3 files changed, 89 insertions(+), 8 deletions(-)
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 0a5b54034d4b..1047149ac2a4 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_set_desc_cache(struct virtio_device *dev, u32 thr)
+{
+ dev->desc_cache_thr = thr;
+}
+EXPORT_SYMBOL_GPL(virtio_set_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..0ebcd4f12d3b 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -117,6 +117,15 @@ struct vring_virtqueue {
/* Hint for event idx: already triggered no need to disable. */
bool event_triggered;
+ /* desc cache threshold
+ * 0 - disable desc cache
+ * > 0 - enable desc cache. As the threshold of the desc cache.
+ */
+ u32 desc_cache_thr;
+
+ /* desc cache chain */
+ struct list_head desc_cache;
+
union {
/* Available for split ring */
struct {
@@ -423,7 +432,53 @@ 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_free(struct list_head *head)
+{
+ struct list_head *n, *pos;
+
+ BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_desc));
+ BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_packed_desc));
+
+ list_for_each_prev_safe(pos, n, head)
+ kfree(pos);
+}
+
+static void __desc_cache_put(struct vring_virtqueue *vq,
+ struct list_head *node, int n)
+{
+ if (n <= vq->desc_cache_thr)
+ list_add(node, &vq->desc_cache);
+ 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_thr)
+ return kmalloc_array(n, size, gfp);
+
+ if (!list_empty(&vq->desc_cache)) {
+ node = vq->desc_cache.next;
+ list_del(node);
+ return node;
+ }
+
+ return kmalloc_array(vq->desc_cache_thr, size, gfp);
+}
+
+#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 +492,12 @@ 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 +563,7 @@ 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 +707,7 @@ 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 +772,7 @@ 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 +784,12 @@ 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;
@@ -2199,6 +2256,9 @@ 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_thr = vdev->desc_cache_thr;
+
+ INIT_LIST_HEAD(&vq->desc_cache);
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
@@ -2329,6 +2389,7 @@ 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->desc_cache);
}
kfree(vq);
}
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 41edbc01ffa4..bda6f9853e97 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -118,6 +118,7 @@ struct virtio_device {
struct list_head vqs;
u64 features;
void *priv;
+ u32 desc_cache_thr;
};
static inline struct virtio_device *dev_to_virtio(struct device *_dev)
@@ -130,6 +131,19 @@ int register_virtio_device(struct virtio_device *dev);
void unregister_virtio_device(struct virtio_device *dev);
bool is_virtio_device(struct device *dev);
+/**
+ * virtio_set_desc_cache - set virtio ring desc cache threshold
+ *
+ * virtio will cache the allocated indirect desc.
+ *
+ * This function must be called before find_vqs.
+ *
+ * @thr:
+ * 0 - disable desc cache
+ * > 0 - enable desc cache. As the threshold of the desc cache.
+ */
+void virtio_set_desc_cache(struct virtio_device *dev, u32 thr);
+
void virtio_break_device(struct virtio_device *dev);
void virtio_config_changed(struct virtio_device *dev);
--
2.31.0
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 at linux.alibaba.com>
---
drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0ebcd4f12d3b..e6d1985a87a8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1089,7 +1089,11 @@ static void vring_unmap_desc_packed(const struct
vring_virtqueue *vq,
}
}
-static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
+#define desc_cache_get_packed(vq, n, gfp) \
+ _desc_cache_get(vq, n, gfp, struct vring_packed_desc)
+
+static struct vring_packed_desc *alloc_indirect_packed(struct vring_virtqueue
*vq,
+ unsigned int total_sg,
gfp_t gfp)
{
struct vring_packed_desc *desc;
@@ -1101,7 +1105,7 @@ static struct vring_packed_desc
*alloc_indirect_packed(unsigned int total_sg,
*/
gfp &= ~__GFP_HIGHMEM;
- desc = kmalloc_array(total_sg, sizeof(struct vring_packed_desc), gfp);
+ desc = desc_cache_get_packed(vq, total_sg, gfp);
return desc;
}
@@ -1121,7 +1125,7 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
dma_addr_t addr;
head = vq->packed.next_avail_idx;
- desc = alloc_indirect_packed(total_sg, gfp);
+ desc = alloc_indirect_packed(vq, total_sg, gfp);
if (unlikely(vq->vq.num_free < 1)) {
pr_debug("Can't add buf len 1 - avail = 0\n");
@@ -1212,7 +1216,7 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
for (i = 0; i < err_idx; i++)
vring_unmap_desc_packed(vq, &desc[i]);
- kfree(desc);
+ desc_cache_put(vq, desc, total_sg);
END_USE(vq);
return -ENOMEM;
@@ -1437,20 +1441,22 @@ static void detach_buf_packed(struct vring_virtqueue
*vq,
}
if (vq->indirect) {
- u32 len;
+ u32 len, n;
/* Free the indirect table, if any, now that it's unmapped. */
desc = state->indir_desc;
if (!desc)
return;
+ len = vq->packed.desc_extra[id].len;
+ n = len / sizeof(struct vring_packed_desc);
+
if (vq->use_dma_api) {
- len = vq->packed.desc_extra[id].len;
- for (i = 0; i < len / sizeof(struct vring_packed_desc);
- i++)
+ for (i = 0; i < n; i++)
vring_unmap_desc_packed(vq, &desc[i]);
}
- kfree(desc);
+
+ desc_cache_put(vq, desc, n);
state->indir_desc = NULL;
} else if (ctx) {
*ctx = state->indir_desc;
@@ -1768,6 +1774,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
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_thr = vdev->desc_cache_thr;
+
+ INIT_LIST_HEAD(&vq->desc_cache);
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
@@ -2389,8 +2398,8 @@ 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->desc_cache);
}
+ desc_cache_free(&vq->desc_cache);
kfree(vq);
}
EXPORT_SYMBOL_GPL(vring_del_virtqueue);
--
2.31.0
If the VIRTIO_RING_F_INDIRECT_DESC negotiation succeeds, and the number
of sgs used for sending packets is greater than 1. We must constantly
call __kmalloc/kfree to allocate/release desc.
In the case of extremely fast package delivery, the overhead cannot be
ignored:
27.46% [kernel] [k] virtqueue_add
16.66% [kernel] [k] detach_buf_split
16.51% [kernel] [k] virtnet_xsk_xmit
14.04% [kernel] [k] virtqueue_add_outbuf
5.18% [kernel] [k] __kmalloc
4.08% [kernel] [k] kfree
2.80% [kernel] [k] virtqueue_get_buf_ctx
2.22% [kernel] [k] xsk_tx_peek_desc
2.08% [kernel] [k] memset_erms
0.83% [kernel] [k] virtqueue_kick_prepare
0.76% [kernel] [k] virtnet_xsk_run
0.62% [kernel] [k] __free_old_xmit_ptr
0.60% [kernel] [k] vring_map_one_sg
0.53% [kernel] [k] native_apic_mem_write
0.46% [kernel] [k] sg_next
0.43% [kernel] [k] sg_init_table
0.41% [kernel] [k] kmalloc_slab
Compared to not using virtio indirect cache, virtio-net can get a 16%
performance improvement when using indirect desc cache.
In the test case, the CPU where the package is sent has reached 100%.
The following are the PPS in two cases:
indirect desc cache | no cache
3074658 | 2685132
3111866 | 2666118
3152527 | 2653632
3125867 | 2669820
3027147 | 2644464
3069211 | 2669777
3038522 | 2675645
3034507 | 2671302
3102257 | 2685504
3083712 | 2692800
3051771 | 2676928
3080684 | 2695040
3147816 | 2720876
3123887 | 2705492
3180963 | 2699520
3191579 | 2676480
3161670 | 2686272
3189768 | 2692588
3174272 | 2686692
3143434 | 2682416
Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
drivers/net/virtio_net.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4ad25a8b0870..e1ade176ab46 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -31,6 +31,13 @@ module_param(csum, bool, 0444);
module_param(gso, bool, 0444);
module_param(napi_tx, bool, 0644);
+/**
+ * Because virtio desc cache will increase memory overhead, users can turn it
+ * off or select an acceptable value. The maximum value is 2 + MAX_SKB_FRAGS.
+ */
+static u32 virtio_desc_cache_thr = 4;
+module_param(virtio_desc_cache_thr, uint, 0644);
+
/* FIXME: MTU in config. */
#define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
#define GOOD_COPY_LEN 128
@@ -3214,6 +3221,11 @@ static int virtnet_probe(struct virtio_device *vdev)
vi->curr_queue_pairs = num_online_cpus();
vi->max_queue_pairs = max_queue_pairs;
+ if (virtio_desc_cache_thr > 2 + MAX_SKB_FRAGS)
+ virtio_set_desc_cache(vdev, 2 + MAX_SKB_FRAGS);
+ else
+ virtio_set_desc_cache(vdev, virtio_desc_cache_thr);
+
/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
err = init_vqs(vi);
if (err)
--
2.31.0
Michael S. Tsirkin
2021-Nov-01 08:33 UTC
[PATCH v2 3/3] virtio-net: enable virtio indirect cache
On Thu, Oct 28, 2021 at 06:49:19PM +0800, Xuan Zhuo wrote:> If the VIRTIO_RING_F_INDIRECT_DESC negotiation succeeds, and the number > of sgs used for sending packets is greater than 1. We must constantly > call __kmalloc/kfree to allocate/release desc. > > In the case of extremely fast package delivery, the overhead cannot be > ignored: > > 27.46% [kernel] [k] virtqueue_add > 16.66% [kernel] [k] detach_buf_split > 16.51% [kernel] [k] virtnet_xsk_xmit > 14.04% [kernel] [k] virtqueue_add_outbuf > 5.18% [kernel] [k] __kmalloc > 4.08% [kernel] [k] kfree > 2.80% [kernel] [k] virtqueue_get_buf_ctx > 2.22% [kernel] [k] xsk_tx_peek_desc > 2.08% [kernel] [k] memset_erms > 0.83% [kernel] [k] virtqueue_kick_prepare > 0.76% [kernel] [k] virtnet_xsk_run > 0.62% [kernel] [k] __free_old_xmit_ptr > 0.60% [kernel] [k] vring_map_one_sg > 0.53% [kernel] [k] native_apic_mem_write > 0.46% [kernel] [k] sg_next > 0.43% [kernel] [k] sg_init_table > 0.41% [kernel] [k] kmalloc_slab > > Compared to not using virtio indirect cache, virtio-net can get a 16% > performance improvement when using indirect desc cache. > > In the test case, the CPU where the package is sent has reached 100%. > The following are the PPS in two cases: > > indirect desc cache | no cache > 3074658 | 2685132 > 3111866 | 2666118 > 3152527 | 2653632 > 3125867 | 2669820 > 3027147 | 2644464 > 3069211 | 2669777 > 3038522 | 2675645 > 3034507 | 2671302 > 3102257 | 2685504 > 3083712 | 2692800 > 3051771 | 2676928 > 3080684 | 2695040 > 3147816 | 2720876 > 3123887 | 2705492 > 3180963 | 2699520 > 3191579 | 2676480 > 3161670 | 2686272 > 3189768 | 2692588 > 3174272 | 2686692 > 3143434 | 2682416 > > Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com> > --- > drivers/net/virtio_net.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 4ad25a8b0870..e1ade176ab46 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -31,6 +31,13 @@ module_param(csum, bool, 0444); > module_param(gso, bool, 0444); > module_param(napi_tx, bool, 0644); > > +/** > + * Because virtio desc cache will increase memory overhead, users can turn it > + * off or select an acceptable value. The maximum value is 2 + MAX_SKB_FRAGS. > + */Maybe add code to validate it and cap it at acceptable values then.> +static u32 virtio_desc_cache_thr = 4;Wouldn't something like CACHE_LINE_SIZE make more sense here?> +module_param(virtio_desc_cache_thr, uint, 0644); > + > /* FIXME: MTU in config. */ > #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN) > #define GOOD_COPY_LEN 128> @@ -3214,6 +3221,11 @@ static int virtnet_probe(struct virtio_device *vdev) > vi->curr_queue_pairs = num_online_cpus(); > vi->max_queue_pairs = max_queue_pairs; > > + if (virtio_desc_cache_thr > 2 + MAX_SKB_FRAGS) > + virtio_set_desc_cache(vdev, 2 + MAX_SKB_FRAGS); > + else > + virtio_set_desc_cache(vdev, virtio_desc_cache_thr); > + > /* Allocate/initialize the rx/tx queues, and invoke find_vqs */ > err = init_vqs(vi); > if (err) > -- > 2.31.0
Michael S. Tsirkin
2021-Nov-01 08:35 UTC
[PATCH v2 1/3] virtio: cache indirect desc for split
On Thu, Oct 28, 2021 at 06:49:17PM +0800, Xuan Zhuo wrote:> 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 at linux.alibaba.com> > --- > drivers/virtio/virtio.c | 6 +++ > drivers/virtio/virtio_ring.c | 77 ++++++++++++++++++++++++++++++++---- > include/linux/virtio.h | 14 +++++++ > 3 files changed, 89 insertions(+), 8 deletions(-) > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > index 0a5b54034d4b..1047149ac2a4 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_set_desc_cache(struct virtio_device *dev, u32 thr) > +{ > + dev->desc_cache_thr = thr; > +} > +EXPORT_SYMBOL_GPL(virtio_set_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..0ebcd4f12d3b 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -117,6 +117,15 @@ struct vring_virtqueue { > /* Hint for event idx: already triggered no need to disable. */ > bool event_triggered; > > + /* desc cache threshold > + * 0 - disable desc cache > + * > 0 - enable desc cache. As the threshold of the desc cache. > + */ > + u32 desc_cache_thr; > + > + /* desc cache chain */ > + struct list_head desc_cache; > + > union { > /* Available for split ring */ > struct { > @@ -423,7 +432,53 @@ 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_free(struct list_head *head) > +{ > + struct list_head *n, *pos; > + > + BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_desc)); > + BUILD_BUG_ON(sizeof(struct list_head) > sizeof(struct vring_packed_desc)); > + > + list_for_each_prev_safe(pos, n, head) > + kfree(pos); > +} > + > +static void __desc_cache_put(struct vring_virtqueue *vq, > + struct list_head *node, int n) > +{ > + if (n <= vq->desc_cache_thr) > + list_add(node, &vq->desc_cache); > + 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_thr) > + return kmalloc_array(n, size, gfp); > + > + if (!list_empty(&vq->desc_cache)) { > + node = vq->desc_cache.next; > + list_del(node); > + return node; > + } > + > + return kmalloc_array(vq->desc_cache_thr, size, gfp); > +} > + > +#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 +492,12 @@ 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 +563,7 @@ 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 +707,7 @@ 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 +772,7 @@ 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 +784,12 @@ 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; > @@ -2199,6 +2256,9 @@ 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_thr = vdev->desc_cache_thr; > + > + INIT_LIST_HEAD(&vq->desc_cache); > > if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM)) > vq->weak_barriers = false; > @@ -2329,6 +2389,7 @@ 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->desc_cache); > } > kfree(vq); > } > diff --git a/include/linux/virtio.h b/include/linux/virtio.h > index 41edbc01ffa4..bda6f9853e97 100644 > --- a/include/linux/virtio.h > +++ b/include/linux/virtio.h > @@ -118,6 +118,7 @@ struct virtio_device { > struct list_head vqs; > u64 features; > void *priv; > + u32 desc_cache_thr; > }; > > static inline struct virtio_device *dev_to_virtio(struct device *_dev) > @@ -130,6 +131,19 @@ int register_virtio_device(struct virtio_device *dev); > void unregister_virtio_device(struct virtio_device *dev); > bool is_virtio_device(struct device *dev); > > +/** > + * virtio_set_desc_cache - set virtio ring desc cache threshold > + * > + * virtio will cache the allocated indirect desc. > + * > + * This function must be called before find_vqs. > + * > + * @thr: > + * 0 - disable desc cache > + * > 0 - enable desc cache. As the threshold of the desc cache. > + */ > +void virtio_set_desc_cache(struct virtio_device *dev, u32 thr); > +Would a better API be a cache size in bytes? This controls how much memory is spent after all.> void virtio_break_device(struct virtio_device *dev); > > void virtio_config_changed(struct virtio_device *dev); > -- > 2.31.0