[dpdk-dev] [PATCH 4/5] vhost: do not use rte_memcpy for virtio_hdr copy
Yuanhan Liu
yuanhan.liu at linux.intel.com
Thu Dec 3 07:06:12 CET 2015
First of all, rte_memcpy() is mostly useful for coping big packets
by leveraging hardware advanced instructions like AVX. But for virtio
net hdr, which is 12 bytes at most, invoking rte_memcpy() will not
introduce any performance boost.
And, to my suprise, rte_memcpy() is huge. Since rte_memcpy() is
inlined, it takes more space every time we call it at a different
place. Replacing the two rte_memcpy() with directly copy saves
nearly 12K bytes of code size!
# without this patch
$ size /path/to/vhost_rxtx.o
text data bss dec hex filename
36171 0 0 36171 8d4b /path/to/vhost_rxtx.o
# with this patch
$ size /path/to/vhost_rxtx.o
text data bss dec hex filename
24179 0 0 24179 5e73 /path/to/vhost_rxtx.o
Signed-off-by: Yuanhan Liu <yuanhan.liu at linux.intel.com>
---
lib/librte_vhost/vhost_rxtx.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
index 7464b6b..1e0a24e 100644
--- a/lib/librte_vhost/vhost_rxtx.c
+++ b/lib/librte_vhost/vhost_rxtx.c
@@ -70,14 +70,17 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint32_t cpy_len;
struct vring_desc *desc;
uint64_t desc_addr;
- struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
+ struct virtio_net_hdr_mrg_rxbuf hdr = {{0, 0, 0, 0, 0, 0}, 0};
desc = &vq->desc[desc_idx];
desc_addr = gpa_to_vva(dev, desc->addr);
rte_prefetch0((void *)(uintptr_t)desc_addr);
- rte_memcpy((void *)(uintptr_t)desc_addr,
- (const void *)&virtio_hdr, vq->vhost_hlen);
+ if (vq->vhost_hlen == sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
+ *(struct virtio_net_hdr_mrg_rxbuf *)(uintptr_t)desc_addr = hdr;
+ } else {
+ *(struct virtio_net_hdr *)(uintptr_t)desc_addr = hdr.hdr;
+ }
PRINT_PACKET(dev, (uintptr_t)desc_addr, vq->vhost_hlen, 0);
desc_offset = vq->vhost_hlen;
@@ -340,7 +343,7 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
uint16_t res_start_idx, uint16_t res_end_idx,
struct rte_mbuf *pkt)
{
- struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
+ struct virtio_net_hdr_mrg_rxbuf hdr = {{0, 0, 0, 0, 0, 0}, 0};
uint32_t vec_idx = 0;
uint16_t cur_idx = res_start_idx;
uint64_t desc_addr;
@@ -361,13 +364,16 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
rte_prefetch0((void *)(uintptr_t)desc_addr);
- virtio_hdr.num_buffers = res_end_idx - res_start_idx;
+ hdr.num_buffers = res_end_idx - res_start_idx;
LOG_DEBUG(VHOST_DATA, "(%"PRIu64") RX: Num merge buffers %d\n",
dev->device_fh, virtio_hdr.num_buffers);
- rte_memcpy((void *)(uintptr_t)desc_addr,
- (const void *)&virtio_hdr, vq->vhost_hlen);
+ if (vq->vhost_hlen == sizeof(struct virtio_net_hdr_mrg_rxbuf)) {
+ *(struct virtio_net_hdr_mrg_rxbuf *)(uintptr_t)desc_addr = hdr;
+ } else {
+ *(struct virtio_net_hdr *)(uintptr_t)desc_addr = hdr.hdr;
+ }
PRINT_PACKET(dev, (uintptr_t)desc_addr, vq->vhost_hlen, 0);
desc_avail = vq->buf_vec[vec_idx].buf_len - vq->vhost_hlen;
--
1.9.0
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