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.
v4:
1. Only allow desc cache when VIRTIO_RING_F_INDIRECT_DESC negotiation is
successful
2. The desc cache threshold can be set for each virtqueue
v3:
pre-allocate per buffer indirect descriptors array
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 desc cache
drivers/net/virtio_net.c | 12 ++-
drivers/virtio/virtio_ring.c | 152 +++++++++++++++++++++++++++++++----
include/linux/virtio.h | 17 ++++
3 files changed, 163 insertions(+), 18 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 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 at linux.alibaba.com>
---
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
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 at linux.alibaba.com>
---
drivers/virtio/virtio_ring.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a4a91c497a83..76a974219ffd 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1092,7 +1092,11 @@ 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;
@@ -1104,7 +1108,7 @@ 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;
}
@@ -1124,7 +1128,7 @@ 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");
@@ -1215,7 +1219,7 @@ 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;
@@ -1440,20 +1444,22 @@ 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;
@@ -1772,6 +1778,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
!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;
@@ -2391,8 +2399,8 @@ 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_free(vq);
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] kfree2.80% [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_slabCompared to not using virtio indirect cache, virtio-net can get a 16% performance improvement when using virtio 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, 11 insertions(+), 1 deletion(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 9ff2ef9dceca..193c8b38433e 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -42,6 +42,9 @@ module_param(csum, bool, 0444); module_param(gso, bool, 0444); module_param(napi_tx, bool, 0644); +static u32 virtio_desc_cache_threshold = MAX_SKB_FRAGS + 2; +module_param(virtio_desc_cache_threshold, uint, 0644); + /* FIXME: MTU in config. */ #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN) #define GOOD_COPY_LEN 128 @@ -3350,10 +3353,10 @@ static unsigned int mergeable_min_buf_len(struct virtnet_info *vi, struct virtqu static int virtnet_find_vqs(struct virtnet_info *vi) { + int i, total_vqs, threshold; vq_callback_t **callbacks; struct virtqueue **vqs; int ret = -ENOMEM; - int i, total_vqs; const char **names; bool *ctx; @@ -3411,10 +3414,17 @@ static int virtnet_find_vqs(struct virtnet_info *vi) vi->dev->features |= NETIF_F_HW_VLAN_CTAG_FILTER; } + threshold = min_t(u32, virtio_desc_cache_threshold, 2 + MAX_SKB_FRAGS); + for (i = 0; i < vi->max_queue_pairs; i++) { vi->rq[i].vq = vqs[rxq2vq(i)]; vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq); vi->sq[i].vq = vqs[txq2vq(i)]; + + if (!vi->mergeable_rx_bufs && vi->big_packets) + virtqueue_set_desc_cache(vi->rq[i].vq, MAX_SKB_FRAGS + 2); + + virtqueue_set_desc_cache(vi->sq[i].vq, threshold); } /* run here: ret == 0. */ -- 2.31.0
Michael S. Tsirkin
2021-Nov-08 13:49 UTC
[PATCH v4 0/3] virtio support cache indirect desc
On Mon, Nov 08, 2021 at 07:49:48PM +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 > > This patch adds a cache function to virtio to cache these allocated indirect > desc instead of constantly allocating and releasing desc.Hmm a bunch of comments got ignored. See e.g. https://lore.kernel.org/r/20211027043851-mutt-send-email-mst%40kernel.org if they aren't relevant add code comments or commit log text explaining the design choice please.> v4: > 1. Only allow desc cache when VIRTIO_RING_F_INDIRECT_DESC negotiation is successful > 2. The desc cache threshold can be set for each virtqueue > > v3: > pre-allocate per buffer indirect descriptors array > > 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 desc cache > > drivers/net/virtio_net.c | 12 ++- > drivers/virtio/virtio_ring.c | 152 +++++++++++++++++++++++++++++++---- > include/linux/virtio.h | 17 ++++ > 3 files changed, 163 insertions(+), 18 deletions(-) > > -- > 2.31.0
Michael S. Tsirkin
2021-Nov-09 13:03 UTC
[PATCH v4 0/3] virtio support cache indirect desc
On Mon, Nov 08, 2021 at 07:49:48PM +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 > > This patch adds a cache function to virtio to cache these allocated indirect > desc instead of constantly allocating and releasing desc. > > v4: > 1. Only allow desc cache when VIRTIO_RING_F_INDIRECT_DESC negotiation is successful > 2. The desc cache threshold can be set for each virtqueue > > v3: > pre-allocate per buffer indirect descriptors arraySo I'm not sure why we are doing that. Did it improve anything?> 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 desc cache > > drivers/net/virtio_net.c | 12 ++- > drivers/virtio/virtio_ring.c | 152 +++++++++++++++++++++++++++++++---- > include/linux/virtio.h | 17 ++++ > 3 files changed, 163 insertions(+), 18 deletions(-) > > -- > 2.31.0