netdev - Re: [PATCH net-next 2/2] net: optimize skb_postpull

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Message-ID: <CANn89iJOH0QtRhDfBzJr3fpJPNCQJhbMqT_8sa+vH_6mmZ7xhw@mail.gmail.com>
Date:   Thu, 2 Dec 2021 12:37:35 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH net-next 2/2] net: optimize skb_postpull_rcsum()

On Thu, Dec 2, 2021 at 11:32 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Thanks Vladimir
>
> I think that maybe the issue is that the initial skb->csum is zero,
> and the csum_parttial(removed_block) is also zero.
>
> But the initial skb->csum should not be zero if you have a non " all
> zero"  frame.
>
> Can you double check this in drivers/net/ethernet/freescale/enetc/enetc.c ?


Yes, I am not sure why the csum is inverted in enetc_get_offloads()

Perhaps

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c
b/drivers/net/ethernet/freescale/enetc/enetc.c
index 504e12554079e306e477b9619f272d6e96527377..72524f14cae0093763f8a3f57b1e08e31bc4df1a
100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -986,7 +986,7 @@ static void enetc_get_offloads(struct enetc_bdr *rx_ring,
        if (rx_ring->ndev->features & NETIF_F_RXCSUM) {
                u16 inet_csum = le16_to_cpu(rxbd->r.inet_csum);

-               skb->csum = csum_unfold((__force __sum16)~htons(inet_csum));
+               skb->csum = csum_unfold((__force __sum16)htons(inet_csum));
                skb->ip_summed = CHECKSUM_COMPLETE;
        }

If this does not work, then maybe :

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c
b/drivers/net/ethernet/freescale/enetc/enetc.c
index 504e12554079e306e477b9619f272d6e96527377..d190faa9a8242f9f3f962dd30b9f4409a83ee697
100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -987,7 +987,8 @@ static void enetc_get_offloads(struct enetc_bdr *rx_ring,
                u16 inet_csum = le16_to_cpu(rxbd->r.inet_csum);

                skb->csum = csum_unfold((__force __sum16)~htons(inet_csum));
-               skb->ip_summed = CHECKSUM_COMPLETE;
+               if (likely(skb->csum))
+                       skb->ip_summed = CHECKSUM_COMPLETE;
        }

        if (le16_to_cpu(rxbd->r.flags) & ENETC_RXBD_FLAG_VLAN) {