Re: Xen unstability on HP Moonshot m400

[Christoffer Dall <christofferdall@gmail.com>]

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On Mon, Mar 23, 2015 at 1:36 PM, Ian Campbell <ian.campbell@citrix.com>
wrote:

> On Sat, 2015-03-21 at 13:34 +0100, Christoffer Dall wrote:
> > Hi,
> >
> > I have been experiencing a problematic crash running Xen on m400 over
> > the last few days.  I already spoke to Ian and Stefano about this, but
> > thought I'd summarize what I've seen so far and loop in a wider
> > audience.
> >
> > The basic setup is this:
> >  - Two m400 nodes, one running Linux bare-metal, the other running
> > Xen.
> >  - The Xen node runs Dom0 and 1 DomU
> >  - The m400 has a Mellanox Connectx-3 PCIe 10G ethernet card with two
> > parts on it
> >  - Dom0 uses NAT forwarding from Dom0's eth0 (which is connected to
> > the internet) and regular bridging to eth1 which is connected to a
> > private VLAN to the bare-metal node
> >  - Dom0 and DomU are configured with 14GB of ram, 4 cpus each
> >  - DomU runs apache2 serving the GCC manual (see
> >
> https://github.com/chazy/kvmperf/blob/master/cmdline_tests/apache_install.sh
> )
> >
> > The bare-metal node runs apache bench, like this: "ab -n 100000 -c 100
> >
> http://secure-web.cisco.com/1r5tZ8-7RF8gHRANwFdizEZzgeMsjxVO0yKbYiV4zy7LeiUfYBXMkFq7FGW_SZ1x-VxdzyK-ErDsOUiQ9z2x-Ny7XkL_loHP8ene_BuNFscGyWmQ3r6CtXAYaZCY4xRmmPT1uJOsZDLMu7j-LfCOGmQDSdBwgW7QYukI2bCtTrXM/http%3A%2F%2F10.10.1.120%2Fgcc%2Findex.html
> "
> >
> > (10.10.1.120 is the DomU IP address of the bridged interface to eth1)
> >
> > What happens now is that the entire Xen node goes down.  I see various
> > errors in the kernel log, some examples:
> > http://pastebin.ubuntu.com/10642148/
> > http://pastebin.ubuntu.com/10642177/
> > http://pastebin.ubuntu.com/10642181/
> > http://pastebin.ubuntu.com/10635573/
> >
> >
> > All Linux kernels are 3.18 plus some tweaks for the m400 cartridge:
> > https://github.com/columbia/linux-kvm-arm/tree/columbia-armvirt-3.18
>
> Is it worth adding
>
> https://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/commit/?id=285994a62c80f1d72c6924282bcb59608098d5ec
> to your kernel? It isn't Xen specific but it's perhaps possible that Xen
> opens the window wider.
>
> How confident are you in
>
> https://github.com/columbia/linux-kvm-arm/commit/5e29cb0478f3d90e4f568d6bea6840960331bcbb
> ?
> (although I suppose you aren't running in ACPI mode if you are running
> Xen?)
>

I'm not confident at all, but Linux (last I checked was v3.19) doesn't boot
without it, so not sure if there's an alternative?  Mark?


>
> If we think the issue might be to do with coherency of foreign mappings
> undergoing i/o from dom0 and we've already ruled out disk (by using a
> loopback mounted rootfs) then it might be worth bodging netback to
> always copy too.
>
> Adding a call to skb_orphan_frags right before the netif_receive_skb in
> drivers/net/xen-netback/netback.c:xenvif_tx_submit is a simple but
> rather inefficient way of doing that (so I hope it doesn't perturb the
> issue).
>

I'll be happy to try this.


>
> Stefano (who is more familiar with the Linux swiotlb side of things than
> me) is travelling this week so he'll be on West coast time, not sure
> when he gets off a plane nor if he's on email anyway (he's at ELC + this
> ARM ACPI thing)
>
>
ok, we'll see what happens.

-Christoffer

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