On Nov 17, 2007 10:33 AM, Denis Shaposhnikov wrote:
> On Sat, 17 Nov 2007 00:42:54 -0500 (EST)
> Mike Andrews 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:

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

But maxopd appears to be set correctly in tcp_input:
mss = min(mss, offer);

/*
* maxopd stores the maximum length of data AND options
* in a segment; maxseg is the amount of data in a normal
* segment. We need to store this value (maxopd) apart
* from maxseg, because now every segment carries options
* and thus we normally have somewhat less data in segments.
*/
tp->t_maxopd = mss;
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