On 3/15/2017 1:50 AM, David Laight wrote:
From: Shannon Nelson
Sent: 14 March 2017 17:25
...
+ if (unlikely(is_multicast_ether_addr(eth_hdr(skb)->h_dest)))
+ dev->stats.multicast++;
I'd guess that:
dev->stats.multicast += is_multicast_ether_addr(eth_hdr(skb)->h_dest);
generates faster code.
Especially if is_multicast_ether_addr(x) is (*x >> 7).
David
Hi David, thanks for the comment. My local instruction level
performance guru is on vacation this week so I can't do a quick check
with him today on this. However, I"m not too worried here since the
inline code for is_multicast_ether_addr() is simply
return 0x01 & addr[0];
and objdump tells me that on sparc it compiles down to a simple single
byte load and compare:
325c: c2 08 80 03 ldub [ %g2 + %g3 ], %g1
3260: 80 88 60 01 btst 1, %g1
3264: 32 60 00 b3 bne,a,pn %xcc, 3530 <vnet_rx_one+0x430>
3268: c2 5c 61 68 ldx [ %l1 + 0x168 ], %g1
dev->stats.multicast++;
I don't think this driver will ever be used on anything bug sparc, so
I'm not worried about how x86 might compile this.
sln
