netdev - [PATCH v4 net-next 6/9] igc: don't reserve excessive XDP_PACKET

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Date:   Wed,  8 Dec 2021 15:06:59 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     intel-wired-lan@...ts.osuosl.org
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
        Jithu Joseph <jithu.joseph@...el.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        KP Singh <kpsingh@...nel.org>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v4 net-next 6/9] 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_costruct_skb().

Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 142c57b7a451..a2e8d43be3a1 100644
--- 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);
-- 
2.33.1