Hey guys,
I have nothing on your code level to add, but.. while investigating this
issue I ran into the guy that originally created the bug (
http://www.freebsd.org/cgi/query-pr.cgi?pr=183390&cat=). In the email
exchange that followed he told me that had found a workaround by running a
specific -STABLE revision:
"Yes, we found a workaround.
We upgraded to the -STABLE branch of the 9.2, so we use this currently:
[root@storagex ~]# uname -a
FreeBSD storagex.lan.granaglia.com 9.2-STABLE FreeBSD 9.2-STABLE #0
r257712: Tue Nov 5 23:02:49 CET 2013
r...@storagex.lan.granaglia.com:/usr/obj/usr/src/sys/GENERIC
amd64"
Maybe this could help you in your quest to hunt this bug down.
On Tue, Mar 25, 2014 at 1:16 PM, Markus Gebert
<markus.geb...@hostpoint.ch>wrote:
>
> On 25.03.2014, at 02:18, Rick Macklem <rmack...@uoguelph.ca> wrote:
>
> > Christopher Forgeron wrote:
> >>
> >>
> >>
> >> This is regarding the TSO patch that Rick suggested earlier. (With
> >> many thanks for his time and suggestion)
> >>
> >>
> >> As I mentioned earlier, it did not fix the issue on a 10.0 system. It
> >> did make it less of a problem on 9.2, but either way, I think it's
> >> not needed, and shouldn't be considered as a patch for testing/etc.
> >>
> >>
> >> Patching TSO to anything other than a max value (and by default the
> >> code gives it IP_MAXPACKET) is confusing the matter, as the packet
> >> length ultimately needs to be adjusted for many things on the fly
> >> like TCP Options, etc. Using static header sizes won't be a good
> >> idea.
> >>
> > If you look at tcp_output(), you'll notice that it doesn't do TSO if
> > there are any options. That way it knows that the TCP/IP header is
> > just hdrlen.
> >
> > If you don't limit the TSO packet (including TCP/IP and ethernet headers)
> > to 64K, then the "ix" driver can't send them, which is the problem
> > you guys are seeing.
> >
> > There are other ways to fix this problem, but they all may introduce
> > issues that reducing if_hw_tsomax by a small amount does not.
> > For example, m_defrag() could be modified to use 4K pagesize clusters,
> > but this might introduce memory fragmentation problems. (I observed
> > what I think are memory fragmentation problems when I switched NFS
> > to use 4K pagesize clusters for large I/O messages.)
> >
> > If setting IP_MAXPACKET to 65518 fixes the problem (no more EFBIG
> > error replies), then that is the size that if_hw_tsomax can be set
> > to (just can't change IP_MAXPACKET, but that is defined for other
> > things). (It just happens that IP_MAXPACKET is what if_hw_tsomax
> > defaults to. It has no other effect w.r.t. TSO.)
> >
> >>
> >> Additionally, it seems that setting nic TSO will/may be ignored by
> >> code like this in sys/netinet/tcp_output.c:
> >>
>
> Is this confirmed or still a 'it seems'? Have you actually seen a
> tp->t_tsomax value in tcp_output() bigger than if_hw_tsomax or was this
> just speculation because the values are stored in different places? (Sorry,
> if you already stated this in another email, it's currently hard to keep
> track of all the information.)
>
> Anyway, this dtrace one-liner should be a good test if other values appear
> in tp->t_tsomax:
>
> # dtrace -n 'fbt::tcp_output:entry / args[0]->t_tsomax != 0 &&
> args[0]->t_tsomax != 65518 / { printf("unexpected tp->t_tsomax: %i\n",
> args[0]->t_tsomax); stack(); }'
>
> Remember to adjust the value in the condition to whatever you're currently
> expecting. The value seems to be 0 for new connections, probably when
> tcp_mss() has not been called yet. So that's seems normal and I have
> excluded that case too. This will also print a kernel stack trace in case
> it sees an unexpected value.
>
>
> > Yes, but I don't know why.
> > The only conjecture I can come up with is that another net driver is
> > stacked above "ix" and the setting for if_hw_tsomax doesn't propagate
> > up. (If you look at the commit log message for r251296, the intent
> > of adding if_hw_tsomax was to allow device drivers to set a smaller
> > tsomax than IP_MAXPACKET.)
> >
> > Are you using any of the "stacked" network device drivers like
> > lagg? I don't even know what the others all are?
> > Maybe someone else can list them?
>
> I guess the most obvious are lagg and vlan (and probably carp on FreeBSD
> 9.x or older).
>
> On request from Jack, we've eliminated lagg and vlan from the picture,
> which gives us plain ixgbe interfaces with no stacked interfaces on top of
> it. And we can still reproduce the problem.
>
>
> Markus
>
>
> >
> > rick
> >>
> >> 10.0 Code:
> >>
> >> 780 if (len > tp->t_tsomax - hdrlen) { !!
> >> 781 len = tp->t_tsomax - hdrlen; !!
> >> 782 sendalot = 1;
> >> 783 }
> >>
> >>
> >>
> >>
> >> I've put debugging here, set the nic's max TSO as per Rick's patch (
> >> set to say 32k), and have seen that tp->t_tsomax == IP_MAXPACKET.
> >> It's being set someplace else, and thus our attempts to set TSO on
> >> the nic may be in vain.
> >>
> >>
> >> It may have mattered more in 9.2, as I see the code doesn't use
> >> tp->t_tsomax in some locations, and may actually default to what the
> >> nic is set to.
> >>
> >> The NIC may still win, I didn't walk through the code to confirm, it
> >> was enough to suggest to me that setting TSO wouldn't fix this
> >> issue.
> >>
> >>
> >> However, this is still a TSO related issue, it's just not one related
> >> to the setting of TSO's max size.
> >>
> >> A 10.0-STABLE system with tso disabled on ix0 doesn't have a single
> >> packet over IP_MAXPACKET in 1 hour of runtime. I'll let it go a bit
> >> longer to increase confidence in this assertion, but I don't want to
> >> waste time on this when I could be logging problem packets on a
> >> system with TSO enabled.
> >>
> >>
> >> Comments are very welcome..
> >>
> >>
> >>
> > _______________________________________________
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>
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--
Met vriendelijke groeten / With kind regards,
Johan Kooijman
T +31(0) 6 43 44 45 27
F +31(0) 162 82 00 01
E m...@johankooijman.com
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