bizarre em + TSO + MSS issue in RELENG_7

[Kip Macy]

On Nov 17, 2007 3:23 PM, Mike Andrews <mandrews at bit0.com> wrote:
>
> On Sat, 17 Nov 2007, Kip Macy wrote:
>
> > On Nov 17, 2007 2:33 PM, Mike Andrews <mandrews at bit0.com> wrote:
> >> On Sat, 17 Nov 2007, Kip Macy wrote:
> >>
> >>> On Nov 17, 2007 10:33 AM, Denis Shaposhnikov <dsh at vlink.ru> wrote:
> >>>> On Sat, 17 Nov 2007 00:42:54 -0500 (EST)
> >>>> Mike Andrews <mandrews at bit0.com> wrote:
> >>>>
> >>>>> Has anyone run into problems with MSS not being respected when using
> >>>>> TSO, specifically on em cards?
> >>>>
> >>>> Yes, I wrote about this problem on the beginning of 2007, see
> >>>>
> >>>>     http://tinyurl.com/3e5ak5
> >>>>
> >>>
> >>> if_em.c:3502
> >>>        /*
> >>>         * Payload size per packet w/o any headers.
> >>>         * Length of all headers up to payload.
> >>>         */
> >>>        TXD->tcp_seg_setup.fields.mss = htole16(mp->m_pkthdr.tso_segsz);
> >>>        TXD->tcp_seg_setup.fields.hdr_len = hdr_len;
> >>>
> >>>
> >>> Please print out the value of tso_segsz here. It appears to be being
> >>> set correctly. The only thing I can think of is that t_maxopd is not
> >>> correct. As tso_segsz is correct here:
> >>
> >>
> >> It repeatedly prints 1368 during a 1 meg file transfer over a connection
> >> with a 1380 MSS.  Any other printf's I can add?  I'm working on a web page
> >> with tcpdump / firewall log output illustrating the issue...
> >
> > Mike -
> > Denis' tcpdump output doesn't show oversized segments, something else
> > appears to be happening there. Can you post your tcpdump output
> > somewhere?
>
>
> URL sent off-list.

       if (tso) {
               m->m_pkthdr.csum_flags = CSUM_TSO;
               m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
       }


Please print the value of maxopd and optlen under "if (tso)" in
tcp_output. I think the calculated optlen may be too small.

 -Kip