[PATCH RFC v2 12/33] hv_netvsc: add XDP frame size to driver

Jesper Dangaard Brouer
2020-04-08T11:51:47Z

The hyperv NIC drivers XDP implementation is rather disappointing as it
will be a slowdown to enable XDP on this driver, given it will allocate a
new page for each packet and copy over the payload, before invoking the
XDP BPF-prog.

The only positive thing it that its easy to determine the xdp.frame_sz.

Then XDP is enabled on this driver, XDP_PASS and XDP_TX will create the
SKB via build_skb (based on the newly allocated page). Now using XDP
frame_sz this will provide more skb_tailroom, which netstack can use for
SKB coalescing (e.g tcp_try_coalesce -> skb_try_coalesce).

Cc: Wei Liu <wei.liu@kernel.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
drivers/net/hyperv/netvsc_bpf.c | 1 +
drivers/net/hyperv/netvsc_drv.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc_bpf.c b/drivers/net/hyperv/netvsc_bpf.c
index b86611041db6..1e0c024b0a93 100644
--- a/drivers/net/hyperv/netvsc_bpf.c
+++ b/drivers/net/hyperv/netvsc_bpf.c
@@ -49,6 +49,7 @@ u32 netvsc_run_xdp(struct net_device *ndev, struct netvsc_channel *nvchan,
xdp_set_data_meta_invalid(xdp);
xdp->data_end = xdp->data + len;
xdp->rxq = &nvchan->xdp_rxq;
+ xdp->frame_sz = PAGE_SIZE;
xdp->handle = 0;

memcpy(xdp->data, data, len);
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index d8e86bdbfba1..651344fea0a5 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -794,7 +794,7 @@ static struct sk_buff *netvsc_alloc_recv_skb(struct net_device *net,
if (xbuf) {
unsigned int hdroom = xdp->data - xdp->data_hard_start;
unsigned int xlen = xdp->data_end - xdp->data;
- unsigned int frag_size = netvsc_xdp_fraglen(hdroom + xlen);
+ unsigned int frag_size = xdp->frame_sz;

skb = build_skb(xbuf, frag_size);