netdev - [PATCH net-next 8/9] ixgbe: don't reserve excessive XDP_PACKET

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Message-Id: <20220131183152.3085432-9-anthony.l.nguyen@intel.com>
Date:   Mon, 31 Jan 2022 10:31:51 -0800
From:   Tony Nguyen <anthony.l.nguyen@...el.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        netdev@...r.kernel.org, anthony.l.nguyen@...el.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        bjorn@...nel.org, maciej.fijalkowski@...el.com,
        michal.swiatkowski@...ux.intel.com, kafai@...com,
        songliubraving@...com, kpsingh@...nel.org, yhs@...com,
        andrii@...nel.org, bpf@...r.kernel.org,
        Sandeep Penigalapati <sandeep.penigalapati@...el.com>
Subject: [PATCH net-next 8/9] ixgbe: don't reserve excessive XDP_PACKET_HEADROOM on XSK Rx to skb

From: Alexander Lobakin <alexandr.lobakin@...el.com>

{__,}napi_alloc_skb() allocates and reserves additional NET_SKB_PAD
+ NET_IP_ALIGN for any skb.
OTOH, ixgbe_construct_skb_zc() currently allocates and reserves
additional `xdp->data - xdp->data_hard_start`, which is
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 to __napi_alloc_skb() and
don't reserve anything. This will give enough headroom for stack
processing.

Fixes: d0bcacd0a130 ("ixgbe: add AF_XDP zero-copy Rx support")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
Tested-by: Sandeep Penigalapati <sandeep.penigalapati@...el.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
index 5447bfb31838..80078762ed24 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
@@ -214,13 +214,11 @@ static struct sk_buff *ixgbe_construct_skb_zc(struct ixgbe_ring *rx_ring,
 	struct sk_buff *skb;
 
 	/* allocate a skb to store the frags */
-	skb = __napi_alloc_skb(&rx_ring->q_vector->napi,
-			       xdp->data_end - xdp->data_hard_start,
+	skb = __napi_alloc_skb(&rx_ring->q_vector->napi, datasize,
 			       GFP_ATOMIC | __GFP_NOWARN);
 	if (unlikely(!skb))
 		return NULL;
 
-	skb_reserve(skb, xdp->data - xdp->data_hard_start);
 	memcpy(__skb_put(skb, datasize), xdp->data, datasize);
 	if (metasize)
 		skb_metadata_set(skb, metasize);
-- 
2.31.1