igc: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb

{__,}napi_alloc_skb() allocates and reserves additional NET_SKB_PAD
+ NET_IP_ALIGN for any skb.
OTOH, igc_construct_skb_zc() currently allocates and reserves
additional `xdp->data_meta - xdp->data_hard_start`, which is about
XDP_PACKET_HEADROOM for XSK frames.
There's no need for that at all as the frame is post-XDP and will
go only to the networking stack core.
Pass the size of the actual data only (+ meta) to
__napi_alloc_skb() and don't reserve anything. This will give
enough headroom for stack processing.
Also, net_prefetch() xdp->data_meta and align the copy size to
speed-up memcpy() a little and better match igc_construct_skb().

Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Tested-by: Nechama Kraus <nechamax.kraus@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 6b51baadee3da444e3ab9c0dcdce7424fcdb2760..b965fb809d84281b43b0b693adc9b1f9c4690abe 100644 (file)
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2446,19 +2446,20 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
 static struct sk_buff *igc_construct_skb_zc(struct igc_ring *ring,
                                            struct xdp_buff *xdp)
 {
+       unsigned int totalsize = xdp->data_end - xdp->data_meta;
        unsigned int metasize = xdp->data - xdp->data_meta;
-       unsigned int datasize = xdp->data_end - xdp->data;
-       unsigned int totalsize = metasize + datasize;
        struct sk_buff *skb;
 
-       skb = __napi_alloc_skb(&ring->q_vector->napi,
-                              xdp->data_end - xdp->data_hard_start,
+       net_prefetch(xdp->data_meta);
+
+       skb = __napi_alloc_skb(&ring->q_vector->napi, totalsize,
                               GFP_ATOMIC | __GFP_NOWARN);
        if (unlikely(!skb))
                return NULL;
 
-       skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
-       memcpy(__skb_put(skb, totalsize), xdp->data_meta, totalsize);
+       memcpy(__skb_put(skb, totalsize), xdp->data_meta,
+              ALIGN(totalsize, sizeof(long)));
+
        if (metasize) {
                skb_metadata_set(skb, metasize);
                __skb_pull(skb, metasize);