On Thu, Mar 01, 2012 at 03:28:13PM +0100, Mike Belopuhov wrote:
> This is a well-known from thib and dlg originally with a length fix
> from yours truly, that marginally doubles througput (from 300kpps to
> 500-600kpps on selected hardware).
>
> The idea is to save an IP header and 8 bytes of payload (good enough
> for tcp state tracking) instead of recommended 68 bytes.
>
> We've been running with this diff for quite some time and haven't seen
> any problems, though there were some concerns in the past. Please
> evaluate it for inclusion once again.
Anyone else actually testing this? Any comments?
> diff --git sys/netinet/ip_input.c sys/netinet/ip_input.c
> index 7fa3d66..28b2b47 100644
> --- sys/netinet/ip_input.c
> +++ sys/netinet/ip_input.c
> @@ -1450,12 +1450,12 @@ int inetctlerrmap[PRC_NCMDS] = {
> void
> ip_forward(struct mbuf *m, int srcrt)
> {
> + struct mbuf mfake, *mcopy = NULL;
> struct ip *ip = mtod(m, struct ip *);
> struct sockaddr_in *sin;
> struct rtentry *rt;
> - int error, type = 0, code = 0, destmtu = 0;
> + int error, type = 0, code = 0, destmtu = 0, fake = 0, len;
> u_int rtableid = 0;
> - struct mbuf *mcopy;
> n_long dest;
>
> dest = 0;
> @@ -1498,13 +1498,18 @@ ip_forward(struct mbuf *m, int srcrt)
> }
>
> /*
> - * Save at most 68 bytes of the packet in case
> - * we need to generate an ICMP message to the src.
> - * Pullup to avoid sharing mbuf cluster between m and mcopy.
> + * Fake an mbuf in case we'll need to generate an ICMP message
> */
> - mcopy = m_copym(m, 0, min(ntohs(ip->ip_len), 68), M_DONTWAIT);
> - if (mcopy)
> - mcopy = m_pullup(mcopy, min(ntohs(ip->ip_len), 68));
> + bzero(&mfake.m_hdr, sizeof(mfake.m_hdr));
> + mfake.m_type = m->m_type;
> + if (m_dup_pkthdr(&mfake, m, M_DONTWAIT) == 0) {
> + mfake.m_data = mfake.m_pktdat;
> + len = ((ip->ip_hl << 2) + min(ntohs(ip->ip_len) -
> + (ip->ip_hl << 2), 8));
> + m_copydata(m, 0, len, mfake.m_pktdat);
> + mfake.m_pkthdr.len = mfake.m_len = len;
> + fake = 1;
> + }
>
> ip->ip_ttl -= IPTTLDEC;
>
> @@ -1553,8 +1558,6 @@ ip_forward(struct mbuf *m, int srcrt)
> else
> goto freecopy;
> }
> - if (mcopy == NULL)
> - goto freert;
>
> switch (error) {
>
> @@ -1604,13 +1607,15 @@ ip_forward(struct mbuf *m, int srcrt)
> goto freecopy;
> }
>
> - icmp_error(mcopy, type, code, dest, destmtu);
> - goto freert;
> + if (fake) {
> + mcopy = m_copym(&mfake, 0, len, M_DONTWAIT);
> + if (mcopy)
> + icmp_error(mcopy, type, code, dest, destmtu);
> + }
>
> freecopy:
> - if (mcopy)
> - m_freem(mcopy);
> - freert:
> + if (fake)
> + m_tag_delete_chain(&mfake);
> #ifndef SMALL_KERNEL
> if (ipmultipath && ipforward_rt.ro_rt &&
> (ipforward_rt.ro_rt->rt_flags & RTF_MPATH)) {
>
>
> --
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