Date: Sun, 18 Nov 2007 14:44:09 +0900 From: Pyun YongHyeon <pyunyh@gmail.com> To: Mike Andrews <mandrews@bit0.com> Cc: Denis Shaposhnikov <dsh@vlink.ru>, Kip Macy <kip.macy@gmail.com>, Mike Silbersack <silby@freebsd.org>, Andre Oppermann <andre@freebsd.org>, freebsd-current@freebsd.org Subject: Re: bizarre em + TSO + MSS issue in RELENG_7 Message-ID: <20071118054409.GA1044@cdnetworks.co.kr> In-Reply-To: <473FBD1A.8010207@bit0.com> References: <20071117003504.R31357@mindcrime.int.bit0.com> <20071117213316.499be43b@vlink.ru> <b1fa29170711171308x62a6371dnbb939748c5c59ae2@mail.gmail.com> <20071117170537.F59492@mindcrime.int.bit0.com> <b1fa29170711171519r65473426s1b9f3d9666ff6a92@mail.gmail.com> <20071117182232.T59492@mindcrime.int.bit0.com> <b1fa29170711171619x24233a3cw4361e0f3ca395e4c@mail.gmail.com> <473F9552.50402@bit0.com> <b1fa29170711171804x36e4ae51ie03d01e4bc0220ac@mail.gmail.com> <473FBD1A.8010207@bit0.com>
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--BOKacYhQ+x31HxR3 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 <mandrews@bit0.com> wrote: > >>Kip Macy wrote: > >>>On Nov 17, 2007 3:23 PM, Mike Andrews <mandrews@bit0.com> wrote: > >>>>On Sat, 17 Nov 2007, Kip Macy wrote: > >>>> > >>>>>On Nov 17, 2007 2:33 PM, Mike Andrews <mandrews@bit0.com> wrote: > >>>>>>On Sat, 17 Nov 2007, Kip Macy wrote: > >>>>>> > >>>>>>>On Nov 17, 2007 10:33 AM, Denis Shaposhnikov <dsh@vlink.ru> wrote: > >>>>>>>>On Sat, 17 Nov 2007 00:42:54 -0500 (EST) > >>>>>>>>Mike Andrews <mandrews@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. 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. -- Regards, Pyun YongHyeon --BOKacYhQ+x31HxR3 Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="em.tso.patch" Index: if_em.c =================================================================== RCS file: /home/ncvs/src/sys/dev/em/if_em.c,v retrieving revision 1.184 diff -u -r1.184 if_em.c --- if_em.c 10 Sep 2007 21:50:40 -0000 1.184 +++ if_em.c 18 Nov 2007 05:42:35 -0000 @@ -1791,6 +1791,7 @@ m_head = *m_headp; /* Do hardware assists */ + txd_upper = txd_lower = 0; if (em_tso_setup(adapter, m_head, &txd_upper, &txd_lower)) /* we need to make a final sentinel transmit desc */ tso_desc = TRUE; --BOKacYhQ+x31HxR3--
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