Date: Sat, 28 Dec 2019 08:33:37 -0500 From: Patrick Kelsey <pkelsey@freebsd.org> To: Vincenzo Maffione <vmaffione@freebsd.org> Cc: Patrick Kelsey <pkelsey@freebsd.org>, Andriy Gapon <avg@freebsd.org>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: vmx: strange issue, related to to tso? Message-ID: <C586E5E0-98B5-4481-8982-2B5509EE5F51@freebsd.org> In-Reply-To: <CA%2B_eA9hMAyrdw=JzMYPxpogUNTBFo5n8-St1KjarcB4tQW6Awg@mail.gmail.com> References: <CA%2B_eA9hMAyrdw=JzMYPxpogUNTBFo5n8-St1KjarcB4tQW6Awg@mail.gmail.com>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236999 appears to be converging to the same issue. If you want to create a review for the proposed patch that would be great. It would be good to have corroborating test results for the proposed patch, something I will probably not be able to try to obtain for at least a couple of days. -Patrick > On Dec 28, 2019, at 3:17 AM, Vincenzo Maffione <vmaffione@freebsd.org> wrote: > > > 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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