Re: [Xen-devel] PCI passthrough issue

[Jean Baptiste Favre <xen-devel@xxxxxxxxxxx>]

Hello,
I think I'll have to read another time "man modprobe" :)
See bellow, I've good news

Le 01/02/2011 16:14, Jean Baptiste Favre a Ãcrit :
> Le 01/02/2011 15:18, Ian Campbell a Ãcrit :
> > On Tue, 2011-02-01 at 14:12 +0000, Jean Baptiste Favre wrote:
> >
> >> Le 01/02/2011 14:20, Ian Campbell a Ãcrit :
> >
> >>>>> If you restrict dom0 to >256MB but <512MB (using dom0_mem= on
> >>> hypervisor
> >>>>> command line) does the NIC work correctly in non-passedthrough form?
> >>>> My Xen hypervisor commandline is as follow:
> >>>> placeholder dom0_mem=256M dom0_max_vcpus=1 dom0_vcpus_pin loglvl=all
> >>>> guest_loglvl=all com1=115200,8n1 console=com1
> >>>>
> >>>> Everything works great without passthrough, but my dom0 is 64bits
> > which
> >>>> may explain that (I do have this strange behaviour only with 32bits
> >>>> kernels).
> >>>
> >>> I don't suppose you could try installing a 32 bit OS in dom0? (e.g.
> > as a
> >>> skanky hack you might fit something into your existing swap
> >>> partition ;-))
> >> I could try, but that would means breaking my test platform. Let's
> say I
> >> prefer complete other tests before :)
> >
> > Sure, no problem.
> >
> >>>> I did not tried changing dom0_mem param.
> >>>>
> >>>>> Similarly does the kernel running native with mem= cause the
> failure?
> >>>> Not sure I understand what you mean here.
> >>>
> >>> I meant to run the system as a native (non-Xen) system and use the
> >>> kernels mem= command line parameter to restrict the system to the
> >>> problematic amounts of memory. Really just trying to verify if
> > something
> >>> is up specifically due to Xen or not. Probably needs a 32 bit
> >>> user/kernel to be a useful experiment.
> >> Ah ok. But then, running 32bits kernel with 64 bits OS will work ? (I
> >> didn't know 64bits kernel worked with 32bits OS before Konrad told me)
> >
> > 32 user on 64 kernel works, 64 user on 32 kernel does not so this will
> > tie in with the 32 bit test above too.
> >
> >>> What do "ifconfig" or "ethtool -S" show for the device after some
> >>> failures. Do any of the numbers increment inline with the dropped
> >>> frames?
> >>>
> >>> Perhaps interestingly 85 bytes, plus the ICMP, IP and Ethernet header
> >>> sizes is something around 128 bytes (depending on options etc).
> This is
> >>> pure numerology but I notice that sky2 has a copybreak parameter
> >>> ("Receive copy threshold") which defaults to 128. I think it would be
> >>> worth trying 64 and 256.
> >> That's exactly the problem I faced with 256mb memory for my domU.
> >> Outgoing packets reached my gateway (tcpdump saw them on it, as well as
> >> replies) but incoming packets greater than 128bits were blocked
> >> somewhere between Xen hypervisor and domU user space (where I was
> >> listening traffic with tcpdump).
> >>
> >> I didn't notice the copybreak from sky2. Where can I change it ? It
> >> could be exactly what we're looking for from the beginning, couldn't
> > it ?
> >> How can I change it ?
> >
> > Assuming the driver is modular:
> >         "modprobe sky2 copybreak=<N>"
> >
> > Depending on your distro there will be somewhere in /etc you can add
> > this. e.g. on Debian you can create a file in /etc/modprobe.d/
> > containing "option sky copybreak=<N>" other distros
> > use /etc/modprobe.conf etc.
> OK I see but it doesn't seems to have any effect.
> I tried "option sky copybreak=0" to get all packet copied with no change.
>
> But I have to say that I'm a bit confused: as I run a PV domU, kernel
> and initrd are provided by dom0.
> So basically, I had no module related binaries installed. After
> installation, I tried to remove module and reload it with different
> configuration without changes.
> Is there any way to provide this sort of option in kernel commandline so
> that it 'll be taken into account even in initrd ?
>
> >>> Are you able to see any traffic with tcpdump, either in guest and/or
> >>> from another host (may require switch configuration to allow it to see
> >>> the traffic). e.g. do you see the ICMP Echo Request but not the Echo
> >>> Response or do you see nothing at all etc.
> >> tcpdump tests have been done from my gateway and from domU.
> >> On the GW: can see all incoming packets (whatever could be the
> size) and
> >> send all replies.
> >> On the DomU: can see all outgoing packets but only incoming ones
> shorter
> >> than 128bytes (global size, means "ping -s85" and less)
> >
> > OK, so it is the sky2 receive path which is at fault, that's very useful
> > info. It corresponds with the copybreak theory too.
OK, just found it:
after domU boot:
- log in
- ping -s 86 10.0.0.1 (fails)
- rmmod sky2
- modprobe sky2 copybreak=0 (no packet copied)
- ping -s 86 10.0.0.1 (works)

So it's clearly related to that option.
Now the question: what am I supposed to do ?
It seems that adding this options in /etc/modprobe.d/sky2.conf does not
work, neither using /etc/modules

Regards,
JB



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