Date: Sat, 28 Dec 2019 09:16:55 +0100 From: Vincenzo Maffione <vmaffione@freebsd.org> To: Patrick Kelsey <pkelsey@freebsd.org> Cc: Andriy Gapon <avg@freebsd.org>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: vmx: strange issue, related to to tso? Message-ID: <CA%2B_eA9hMAyrdw=JzMYPxpogUNTBFo5n8-St1KjarcB4tQW6Awg@mail.gmail.com> In-Reply-To: <CAD44qMVVg2T-LyKXc7Rvf7%2B4iuqmrAVXAoQohjQHkGW97TD4UQ@mail.gmail.com> References: <67dc1ce9-274c-7e70-30dc-97e2d5767237@FreeBSD.org> <CA%2B_eA9jnyKD-JikmOA-uJybCf%2BR_5JLRaZ5GPBhQ=09MnEfwXw@mail.gmail.com> <963e3042-90b4-4de2-e18c-3e29627a25a9@FreeBSD.org> <CAD44qMVVg2T-LyKXc7Rvf7%2B4iuqmrAVXAoQohjQHkGW97TD4UQ@mail.gmail.com>
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I think you are correct. Good catch! We should file a bug and/or create a review on the Phabricator (If you are busy I could do that). Thanks, Vincenzo Il giorno sab 28 dic 2019 alle ore 05:44 Patrick Kelsey <pkelsey@freebsd.org> ha scritto: > > On Fri, Dec 27, 2019 at 5:01 PM Andriy Gapon <avg@freebsd.org> wrote: > >> On 27/12/2019 15:34, Vincenzo Maffione wrote: >> > It may be useful to check what happens if you replace the vmx0 >> interface with an >> > em0. >> > In this way you would know if the issue is vmx-specific or not. >> >> I'll put this on my to-do, can't test right now. >> >> But one thing I noticed when comparing the TCP control block of the >> connection >> before and after the "TSO dance" is that TF_TSO gets cleared after any >> outgoing >> traffic while TSO is disabled on the interface. And the flag does not >> come back >> after TSO is reenabled. Any new connections get the flag, of course. >> >> So, I indeed suspect that there is a problem with vmx TSO. >> As another data point, an older system from before vmx->iflib conversion >> does >> not exhibit the problem. >> >> > Il giorno gio 26 dic 2019 alle ore 20:04 Andriy Gapon <avg@freebsd.org >> > <mailto:avg@freebsd.org>> ha scritto: >> > >> > >> > Maybe someone would have any pointers for me with the following >> problem. >> > This happens with CURRENT as of the beginning of September. >> > I connect via ssh to a VM running on VMware, it has a single vmx0 >> interface. >> > The problem is that when I print a moderately large amount of text >> to the >> > terminal (e.g., tail -100 /var/log/messages) I literally see it >> printed in >> > chunks with noticeable pauses between chunks. It takes several >> seconds for all >> > lines to get shown. This happens every time I do it. >> > There is an interesting twist. If I disable TSO with ifconfig vmx0 >> -tso and >> > print the same output in the same ssh session, then the output is >> smooth and >> > fast as I would expect it. The lines scroll by almost instantly. >> > If then I re-enable TSO and again produce the same output in the >> same ssh, then >> > it is still fast. >> > >> > It appears that the TCP connection gets tuned to some very >> sub-optimal >> > parameters when TSO is enabled. When I disable TSO, the parameters >> get re-tuned >> > to better values and the values stick when I re-enable TSO. >> > This is just a conjecture, of course. >> > >> > I have some tcpdump captures, but I do not see anything that would >> really stand >> > out. One difference is that in the slow case only "full sized" >> packets are sent >> > while in the fast case there are shorter packets with push flag. >> > >> > Some packets for the slow case: >> > 00:00:00.453202 IP 10.180.106.180.22 > 10.180.1.29.25490: Flags >> [.], seq >> > 37:1485, ack 36, win 128, options [nop,nop,TS val 1403195134 ecr >> 4966311], >> > length 1448 >> > 00:00:00.096859 IP 10.180.1.29.25490 > 10.180.106.180.22: Flags >> [.], ack 1485, >> > win 1026, options [nop,nop,TS val 4966864 ecr 1403195134], length 0 >> > 00:00:00.442963 IP 10.180.106.180.22 > 10.180.1.29.25490: Flags >> [.], seq >> > 1485:2933, ack 36, win 128, options [nop,nop,TS val 1403195664 ecr >> 4966864], >> > length 1448 >> > 00:00:00.092677 IP 10.180.1.29.25490 > 10.180.106.180.22: Flags >> [.], ack 2933, >> > win 1026, options [nop,nop,TS val 4967400 ecr 1403195664], length 0 >> > 00:00:00.437336 IP 10.180.106.180.22 > 10.180.1.29.25490: Flags >> [.], seq >> > 2933:4381, ack 36, win 128, options [nop,nop,TS val 1403196194 ecr >> 4967400], >> > length 1448 >> > 00:00:00.097190 IP 10.180.1.29.25490 > 10.180.106.180.22: Flags >> [.], ack 4381, >> > win 1026, options [nop,nop,TS val 4967934 ecr 1403196194], length 0 >> > >> > Some packets after the TSO dance: >> > 00:00:00.000450 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [.], seq >> > 4077:5525, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 1448 >> > 00:00:00.000016 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [P.], seq >> > 5525:6097, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 572 >> > 00:00:00.000009 IP 10.180.1.29.25369 > 10.180.106.180.22: Flags >> [.], ack 5525, >> > win 1003, options [nop,nop,TS val 21706510 ecr 2124310129], length 0 >> > 00:00:00.000303 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [.], seq >> > 6097:7545, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 1448 >> > 00:00:00.000019 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [P.], seq >> > 7545:8117, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 572 >> > 00:00:00.000013 IP 10.180.1.29.25369 > 10.180.106.180.22: Flags >> [.], ack 7545, >> > win 1003, options [nop,nop,TS val 21706510 ecr 2124310129], length 0 >> > 00:00:00.000162 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [.], seq >> > 8117:9565, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 1448 >> > 00:00:00.000012 IP 10.180.106.180.22 > 10.180.1.29.25369: Flags >> [P.], seq >> > 9565:10137, ack 36, win 128, options [nop,nop,TS val 2124310129 ecr >> 21706510], >> > length 572 >> > 00:00:00.000007 IP 10.180.1.29.25369 > 10.180.106.180.22: Flags >> [.], ack 9565, >> > win 1003, options [nop,nop,TS val 21706510 ecr 2124310129], length 0 >> > >> > What else can I examine to debug the problem further? >> > Thank you! >> > -- >> > Andriy Gapon >> > _______________________________________________ >> > freebsd-net@freebsd.org <mailto:freebsd-net@freebsd.org> mailing >> list >> > https://lists.freebsd.org/mailman/listinfo/freebsd-net >> > To unsubscribe, send any mail to " >> freebsd-net-unsubscribe@freebsd.org >> > <mailto:freebsd-net-unsubscribe@freebsd.org>" >> > >> >> > I am not able to test this at the moment, nor likely in the very near > future, but I did have a few minutes to do some code reading and now > believe that the following is part of the problem, if not the entire > problem. Using r353803 as a reference, I believe line 1323 in > sys/dev/vmware/vmxnet3/if_vmx.c (in vmxnet3_isc_txd_encap()) should be: > > sop->hlen = hdrlen + ipi->ipi_tcp_hlen; > > instead of the current: > > sop->hlen = hdrlen; > > This can be seen by going back to r333813 and examining the CSUM_TSO case > of vmxnet3_txq_offload_ctx(). The final increment of *start in that case > is what was literally lost in translation when converting the driver to > iflib. > > -Patrick >
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