This patch aligns the Virtio-net header on a cache-line boundary to
optimize cache utilization, as it puts the Virtio-net header (which
is always accessed) on the same cache line as the packet header.
For example with an application that forwards packets at L2 level,
a single cache-line will be accessed with this patch, instead of
two before.
In case of multi-buffers packets, next segments will be aligned on
a cache-line boundary, instead of cache-line boundary minus size of
vnet header before.
Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
---
Hi,
I send this patch as RFC because I get strange results on SandyBridge.
For micro-benchmarks, I measure a +6% gain on Haswell, but I get a big
performance drop on SandyBridge (~-18%).
When running PVP benchmark on SandyBridge, I measure a +4% performance
gain though.
So I'd like to call for testing on this patch, especially PVP-like testing
on newer architectures.
Regarding SandyBridge, I would be interrested to know whether we should
take the performance drop into account, as we for example had one patch in
last release that cause a performance drop on SB we merged anyway.
Cheers,
Maxime
drivers/net/virtio/virtio_rxtx.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index cab6e8f..ef95dde 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -182,7 +182,6 @@ static inline int
virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf *cookie)
{
struct vq_desc_extra *dxp;
- struct virtio_hw *hw = vq->hw;
struct vring_desc *start_dp;
uint16_t needed = 1;
uint16_t head_idx, idx;
@@ -203,10 +202,8 @@ virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct
rte_mbuf *cookie)
start_dp = vq->vq_ring.desc;
start_dp[idx].addr =
- VIRTIO_MBUF_ADDR(cookie, vq) +
- RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
- start_dp[idx].len =
- cookie->buf_len - RTE_PKTMBUF_HEADROOM + hw->vtnet_hdr_size;
+ VIRTIO_MBUF_ADDR(cookie, vq) + RTE_PKTMBUF_HEADROOM;
+ start_dp[idx].len = cookie->buf_len - RTE_PKTMBUF_HEADROOM;
start_dp[idx].flags = VRING_DESC_F_WRITE;
idx = start_dp[idx].next;
vq->vq_desc_head_idx = idx;
@@ -768,7 +765,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
uint16_t nb_pkts)
}
rxm->port = rxvq->port_id;
- rxm->data_off = RTE_PKTMBUF_HEADROOM;
+ rxm->data_off = RTE_PKTMBUF_HEADROOM + hdr_size;
rxm->ol_flags = 0;
rxm->vlan_tci = 0;
@@ -778,7 +775,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
uint16_t nb_pkts)
rxm->data_len = (uint16_t)(len[i] - hdr_size);
hdr = (struct virtio_net_hdr *)((char *)rxm->buf_addr +
- RTE_PKTMBUF_HEADROOM - hdr_size);
+ RTE_PKTMBUF_HEADROOM);
if (hw->vlan_strip)
rte_vlan_strip(rxm);
@@ -892,13 +889,13 @@ virtio_recv_mergeable_pkts(void *rx_queue,
}
header = (struct virtio_net_hdr_mrg_rxbuf *)((char
*)rxm->buf_addr +
- RTE_PKTMBUF_HEADROOM - hdr_size);
+ RTE_PKTMBUF_HEADROOM);
seg_num = header->num_buffers;
if (seg_num == 0)
seg_num = 1;
- rxm->data_off = RTE_PKTMBUF_HEADROOM;
+ rxm->data_off = RTE_PKTMBUF_HEADROOM + hdr_size;
rxm->nb_segs = seg_num;
rxm->next = NULL;
rxm->ol_flags = 0;
@@ -944,7 +941,7 @@ virtio_recv_mergeable_pkts(void *rx_queue,
while (extra_idx < rcv_cnt) {
rxm = rcv_pkts[extra_idx];
- rxm->data_off = RTE_PKTMBUF_HEADROOM - hdr_size;
+ rxm->data_off = RTE_PKTMBUF_HEADROOM;
rxm->next = NULL;
rxm->pkt_len = (uint32_t)(len[extra_idx]);
rxm->data_len = (uint16_t)(len[extra_idx]);
--
2.9.3
