Re: [PATCH] Revert "net: pskb_trim_rcsum() and...

Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"

From: Andreas Schwab <hidden>
Date: 2018-06-17 10:28:07

On Jun 16 2018, Eric Dumazet [off-list ref] wrote:

quoted hunk

I would try something like :

Basically do not bother using CHECKSUM_COMPLETE for small frames that might have been padded.

Since we need to bring one cache line in eth_type_trans() and further header processing,
computing the checksum in software will be almost free anyway.

diff --git a/drivers/net/ethernet/sun/sungem.c b/drivers/net/ethernet/sun/sungem.c
index 7a16d40a72d13cf1d522e8a3a396c826fe76f9b9..071039f211a8a33153e888bd4014314ba5e686a4 100644
--- a/drivers/net/ethernet/sun/sungem.c
+++ b/drivers/net/ethernet/sun/sungem.c

@@ -855,9 +855,11 @@ static int gem_rx(struct gem *gp, int work_to_do)
                        skb = copy_skb;
                }
 
-               csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
-               skb->csum = csum_unfold(csum);
-               skb->ip_summed = CHECKSUM_COMPLETE;
+               if (len > ETH_ZLEN) {
+                       csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
+                       skb->csum = csum_unfold(csum);
+                       skb->ip_summed = CHECKSUM_COMPLETE;
+               }
                skb->protocol = eth_type_trans(skb, gp->dev);
 
                napi_gro_receive(&gp->napi, skb);

That doesn't change anything.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"

From: Eric Dumazet <hidden>
Date: 2018-06-17 22:54:56


On 06/17/2018 03:27 AM, Andreas Schwab wrote:

That doesn't change anything.

OK, thanks !

Oh this is silly, please try :

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index c642304f178ce0a4e1358d59e45032a39f76fb3f..54dd9c18ecad817812898d6f335e1794a07dabbe 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c

@@ -1845,10 +1845,9 @@ EXPORT_SYMBOL(___pskb_trim);
 int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len)
 {
        if (skb->ip_summed == CHECKSUM_COMPLETE) {
-               int delta = skb->len - len;
+               __wsum csumdiff = skb_checksum(skb, len, skb->len - len, 0);
 
-               skb->csum = csum_sub(skb->csum,
-                                    skb_checksum(skb, len, delta, 0));
+               skb->csum = csum_block_sub(skb->csum, csumdiff, len);
        }
        return __pskb_trim(skb, len);
 }

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