On Fri, Jan 15, 2010 at 5:26 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Changli Gao <xiaosuo@xxxxxxxxx>
> Date: Fri, 15 Jan 2010 17:20:43 +0800
>
> Calling a function is expensive.
>
> What was now a leaf function deep in the call chain, will no longer
> be, so GCC will need to push all live registers onto the stack,
> then reload them back into registers when ipv6_skip_exthdr() returns.
>
> And that function is expensive, it's a lot of code that %99 of the
> time serves no purpose at all.
>
> This will be executed for every single packet we process, and Linux
> can process millions of packets per second, so every cycle and every
> memory reference matters.
>
We can write a new inline function like this:
static inline int ipv6_get_ports(const struct sk_buff *skb, u16 *port1,
u16 *port2)
{
u8 nexthdr;
int hdrlen;
nexthdr = ipv6_hdr(skb)->nexthdr;
hdrlen = sizeof(struct ipv6hdr);
while (1) {
switch (nexthdr) {
case IPPROTO_TCP:
case IPPROTO_UDP:
case IPPROTO_DCCP:
case IPPROTO_ESP:
case IPPROTO_AH:
case IPPROTO_SCTP:
case IPPROTO_UDPLITE:
skb_copy_bits(skb, hdrlen, port1, 2);
skb_copy_bits(skb, hdrlen + 2, port2, 2);
return 0;
case NEXTHDR_HOP:
case NEXTHDR_ROUTING:
case NEXTHDR_FRAGMENT:
case NEXTHDR_AUTH:
case NEXTHDR_DEST:
// some code like ipv6_skip_exthdr()
....
break;
case NEXTHDR_NONE:
return -1;
default:
return -1;
}
}
}
--
Regards，
Changli Gao(xiaosuo@xxxxxxxxx)
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