On Nov 17, 2007 9:44 PM, Pyun YongHyeon wrote:
>
> On Sat, Nov 17, 2007 at 11:18:34PM -0500, Mike Andrews wrote:
> > Kip Macy wrote:
> > >On Nov 17, 2007 5:28 PM, Mike Andrews wrote:
> > >>Kip Macy wrote:
> > >>>On Nov 17, 2007 3:23 PM, Mike Andrews wrote:
> > >>>>On Sat, 17 Nov 2007, Kip Macy wrote:
> > >>>>
> > >>>>>On Nov 17, 2007 2:33 PM, Mike Andrews wrote:
> > >>>>>>On Sat, 17 Nov 2007, Kip Macy wrote:
> > >>>>>>
> > >>>>>>>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:
> > >>>>>>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.
> > >>
> > >>maxopt=1380 - optlen=12 = tso_segsz=1368
> > >>
> > >>Weird though, after this reboot, I had to re-copy a 4 meg file 5 times
> > >>to start getting the firewall to log any drops. Transfer rate was
> > >>around 240KB/sec before the firewall started to drop, then it went down
> > >>to about 64KB/sec during the 5th copy, and stayed there for subsequent
> > >>copies. The actual packet size the firewall said it was dropping was
> > >>varying all over the place still, yet the maxopt/optlen/tso_segsz values
> > >>stayed constant. But it's interesting that it didn't start dropping
> > >>immediately after the reboot -- though the transfer rate was still
> > >>sub-optimal.
> > >
> > >Ok, next theory . You shouldn't be seeing "bad len" packets from
> > >tcpdump. I'm wondering if that means you're sending down more than
> > >64k. Can you please print out the value of mp->m_pkthdr.len around the
> > >same place that you printed out tso_segsz? 64k is the generally
> > >accepted limit for TSO, I'm wondering if the card firmware does
> > >something weird if you give it more.

> >
> > OK. In that last message, where I said it took 5 times to start
> > reproducing the problem... this time it took until I actually toggled
> > TSO back off and back on again, and then it started acting up again. I
> > don't know what the actual trigger is... it's very weird.
> >
> > Initially, w/ TSO on and it wasn't dropping yet (but was still
> > transferring slow)...
> >
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=8306
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=8306
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=8306
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=8306
> > (etc, always 8306)
> >
> > After toggling off/on which caused the drops to start (and the speed to
> > drop even further):
> >
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=7507
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=3053
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1677
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=3037
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=2264
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1656
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1902
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1888
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1640
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1871
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=2461
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=1849
> > BIT0 DEBUG: tso_segsz=1368 hdr_len=66 mp->m_pkthdr.len=2092
> >
> > and so on, with more seemingly random lengths... but none of them ever
> > over 8306, much less 64K.

>
> It seems that em_tso_setup() doesn't clear txd_upper/txd_lower in
> failure path so that unintialized value could be used in subsequent
> Tx descriptor setup.
> How about clearing those variable?(Patch attached)
>
> It seems that em(4) uses EM_TSO_SIZE(64K) to create DMA tag. A packet
> can have 64K payload under TSO so its the mximum size of the mbuf
> chain would be 64K + sizeof(link layer). So I guess the EM_TSO_SIZE
> should be increased to hold sizeof(link layer).
> It had been a long time since I looked into em(4) so I'm not sure.


Huh? They are set to 0 on entry, and not touched again before you go
into the setup routine, your change has no effect.

Jack
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