[PATCH net-next v4 12/33] hv_netvsc: add XDP frame size to driver

[Jesper Dangaard Brouer <brouer@redhat.com>]

The hyperv NIC driver does memory allocation and copy even without XDP.
In XDP mode it will allocate a new page for each packet and copy over
the payload, before invoking the XDP BPF-prog.

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

The XDP implementation for hv_netvsc transparently passes xdp_prog
to the associated VF NIC. Many of the Azure VMs are using SRIOV, so
majority of the data are actually processed directly on the VF driver's XDP
path. So the overhead of the synthetic data path (hv_netvsc) is minimal.

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).

V3: Adjust patch desc to be more positive.

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 5de57fc3ec60..6267f706e8ee 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -795,7 +795,7 @@ 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);