bizarre em + TSO + MSS issue in RELENG_7

[Mike Andrews]

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...