On Nov 18, 2007 11:33 AM, Jack Vogel <jfvogel_at_gmail.com> wrote: > > On Nov 18, 2007 12:58 AM, Mike Andrews <mandrews_at_bit0.com> wrote: > > > > On Sat, 17 Nov 2007, Mike Andrews wrote: > > > > > Kip Macy wrote: > > >> On Nov 17, 2007 5:28 PM, Mike Andrews <mandrews_at_bit0.com> wrote: > > >>> Kip Macy wrote: > > >>>> 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. > > >>> > > >>> 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 :D. 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. > > > > > > Got a few more data points here. > > > > I can reproduce this on an i386 kernel, so it isn't amd64 specific. > > > > I can reproduce this on an 82541EI nic, so it isn't 82573 specific. > > > > I can't reproduce this on a Marvell Yukon II (msk) nic; it works fine > > whether TSO is on or off. > > > > I can't reproduce this on a bge nic because it doesn't support TSO :) > > That's the only other gigabit nic I've got easy access to. > > > > I can reproduce this with just a Cisco 877W IOS-based router and no Cisco > > PIX / ASA firewalls in the way, with the servers on the LAN interface with > > "ip tcp adjust-mss 1340" on it, and the downloading client on the Cisco's > > 802.11G interface. This time, the client is a Macbook Pro running > > Leopard, and I'm running "tcpdump -i en1 -s 1500 -n -v length \> 1394" on > > the Macbook (not the server this time) to find oversize packets, which is > > actually handier because I can see how trashed they really get :) > > > > I can't reproduce this between two machines on the same subnet (though I > > can reproduce throughput problems alone). I haven't tried lowering the > > system MSS on one end yet (is there a sysctl to lower the MSS for outbound > > connections without lowering the MTU as well?). If I could do this it > > would greatly simplify testing for everyone as they wouldn't have to stick > > an MSS-clamping router in the middle. It doesn't have to be Cisco. > > > > With this setup, copying to the Mac through the 877W from: > > > > msk-based server, TSO disabled: tcpdump reports no problems, file > > transfers are fast > > > > msk-based server, TSO enabled: tcpdump reports no problems, file > > transfers are fast > > > > em-based server, TSO disabled: tcpdump reports no problems, file > > transfers are fast > > > > em-based server, TSO enabled: tcpdump reports numerous oversize packets of > > varying sizes just as before, AND numerous packets with bad TCP checksums. > > The checksum problems aren't limited to only the large packets though. > > (That's probably what's causing the throughput problems.) Toggling rxcsum > > and txcsum flags on the server made no difference. What I haven't tried > > yet is hexdumping the packets to see what exactly is getting trashed. > > > > The problem still comes and goes; sometimes it'll work for a few minutes > > after boot, sometimes not; it might be dependent on what other traffic's > > going through the box. > > Hmmm, OK so the data is pointing to something in the em TSO or encap > code. I will look into this tomorrow. So the necessary elements are systems > on two subnets and em doing the transmitting with TSO? BTW, not to dodge the problem, but this is a case where I'd say its absurd to be using TSO. Is the link at 1G or 100Mb? Nevertheless it does point to a real bug in the code. JackReceived on Sun Nov 18 2007 - 18:40:19 UTC
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