Packet corruption in re0 [checksum offloading]

Sam Leffler sam at errno.com
Sat Feb 23 18:36:04 UTC 2008


Pyun YongHyeon wrote:
> On Fri, Feb 22, 2008 at 10:43:22AM +0200, Ian FREISLICH wrote:
>  > Pyun YongHyeon wrote:
>  > > On Thu, Feb 21, 2008 at 01:18:18PM +0200, Ian FREISLICH wrote:
>  > >  > Pyun YongHyeon wrote:
>  > >  > > On Thu, Feb 21, 2008 at 02:47:43PM +1000, Robert Backhaus wrote:
>  > >  > >  > On Thu, Feb 21, 2008 at 1:50 PM, Pyun YongHyeon <pyunyh at gmail.com> wr
>  > ote:
>  > >  > >  > > On Thu, Feb 21, 2008 at 11:03:02AM +1000, Robert Backhaus wrote:
>  > >  > >  > >   > I am experiencing roughly 15% packet corruption on the re inter
>  > face 
>  > >  > on
>  > >  > >  > >   > my freebsd 7/amd64  box.
>  > >  > >  > >   >
>  > >  > >  > >   > FreeBSD gw.flexi.robbak.com 7.0-PRERELEASE FreeBSD 7.0-PRERELEA
>  > SE #8
>  > >  > :
>  > >  > >  > >   > Tue Feb  5 09:49:55 EST 2008
>  > >  > >  > >   > root at gw.flexi.robbak.com:/usr/obj/usr/src/sys/GW  amd64
>  > >  > >  > >   >
>  > >  > >  > >   > Just to make troubleshooting difficult, this problem only shows
>  >  up
>  > >  > >  > >   > after the system has been up for roughly 36 hours, depending on
>  >  the
>  > >  > >  > >   > amount of traffic.
>  > >  > >  > >   >
>  > >  > >  > >
>  > >  > >  > >  I didn't take a look attached tcpdump files but I guess the
>  > >  > >  > >  instability issue was fixed in HEAD. It's not yet MFCed but
>  > >  > >  > >  I'll handle it in a week.
>  > >  > >  > >
>  > >  > >  > >  Would you try re(4) in HEAD?
>  > >  > >  > >
>  > >  > >  > 
>  > >  > >  > OK, I'll do that. What is the best way to do that? csupping to "." se
>  > ems a
>  > >  > >  > bit drastic, and I don't do much with cvs proper. I take it that I sh
>  > ould 
>  > >  > use
>  > >  > >  > anon-cvs to grab the directory, but I don't quite know how.
>  > >  > >  > 
>  > >  > > 
>  > >  > > Copy sys/dev/re/if_re.c, sys/pci/if_rlreg.h in HEAD to your box.
>  > >  > > Due to lack of m_defrag(9) in 7-PRERELEASE/RC, you also have to add
>  > >  > > that function to if_re.c(Copy m_defrag() in sys/kern/uipc_mbuf.c on
>  > >  > > HEAD/RELENG_7 to if_re.c). That would make it build on your box.
>  > >  > 
>  > >  > This doesn't solve the problem that I'm seeing on re(4) interfaces.
>  > >  > It basically shows up as quagga establishing OSPF neighours as
>  > >  > "Exchange/DR" when VLAN hardware tagging is enabled.  I'm running
>  > >  > OSPF over 802.1Q vlans.  Neighbours are correctly negotiated once
>  > >  > VLAN hardware tagging is disabled on the interface.
>  > >  > 
>  > >  > I'll do more debugging.
>  > >  > 
>  > > 
>  > > Hmm. That sounds like different issue to me. I guess I din't change
>  > > any semantics in VLAN H/W tagging. Do you still the same VLAN H/W
>  > > tagging related issues on RELENG_7?
>  > > 
>  > > To narrow down the issue it would be even better to know which parts
>  > > of H/W assistance was broken. For example,
>  > >  - Disable checksum offload for VLAN interface first and check
>  > >    whether quagga works.
>  > 
>  > You can only disable offload on the parent interface.
>  > 
>
> Hmm... I thought it should work.
> I have no idea why ioctl handler of vlan(4) rejects checksum
> offload configutation. I guess vlan(4) should be teached to handle
> this. If parent interface have IFCAP_VLAN_HWCSUM capability and
> IFCAP_VLAN_HWTAGGING, ifconfig(4) should be able to control checksum
> offload for vlan(4) interface. CCed to yar to get his opinions on
> controlling checksum offload on vlan(4).
>
>  > >  - Disable checksum offload for parent interface and check again.
>  > > If you can post tcpdump output for broken conntection it may help a
>  > > lot to diagnose the issue.
>  > 
>  > The only flag affecting this behaviour is vlanhwtag.  Various
>  > permutations of the interface flags make no difference to this
>  > behaviour as long as hardware tagging is enabled.
>  > 
>
> Disabling VLAN HW tagging also turns off checksum offload on vlan(4)
> interface.
>
>   

This reminds me that there are several places in the system where h/w 
checksum offload needs to be specially handled but instead is disabled 
as a WAR.  In particular I'm thinking of the bridge where txcsum is 
muted on devices while they are plumbed.  But this can be a big loss and 
the better approach (IMO) is to fill in the missing capability in s/w.

Not sure what components there are besides bridge and vlan; maybe lagg?  
netgraph?

Note there are other capabilities besides checksum offload, TSO can be 
done in s/w with good effect.

    Sam



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