Date: Sat, 17 Nov 2007 18:04:08 -0800 From: "Kip Macy" <kip.macy@gmail.com> To: "Mike Andrews" <mandrews@bit0.com> Cc: Denis Shaposhnikov <dsh@vlink.ru>, 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: <b1fa29170711171804x36e4ae51ie03d01e4bc0220ac@mail.gmail.com> In-Reply-To: <473F9552.50402@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>
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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. Thanks. -Kip
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