[CentOS-virt] NIC Stability Problems Under Xen 4.4 / CentOS 6 / Linux 3.18

[Adi Pircalabu]

On 28/01/17 05:21, Kevin Stange wrote:
> On 01/27/2017 06:08 AM, Karel Hendrych wrote:
>> Have you tried to eliminate all power management features all over?
> 
> I've been trying to find and disable all power management features but
> having relatively little luck with that solving the problems.  Stabbing
> the the dark I've tried different ACPI settings, including completely
> disabling it, disabling CPU frequency scaling, and setting pcie_aspm=off
> on the kernel command line.  Are there other kernel options that might
> be useful to try?

May I chip in here? In our environment we're randomly seeing:

Jan 17 23:40:14 xen01 kernel: ixgbe 0000:04:00.1 eth6: Detected Tx Unit Hang
Jan 17 23:40:14 xen01 kernel:  Tx Queue             <0>
Jan 17 23:40:14 xen01 kernel:  TDH, TDT             <9a>, <127>
Jan 17 23:40:14 xen01 kernel:  next_to_use          <127>
Jan 17 23:40:14 xen01 kernel:  next_to_clean        <98>
Jan 17 23:40:14 xen01 kernel: ixgbe 0000:04:00.1 eth6: 
tx_buffer_info[next_to_clean]
Jan 17 23:40:14 xen01 kernel:  time_stamp           <218443db3>
Jan 17 23:40:14 xen01 kernel:  jiffies              <218445368>
Jan 17 23:40:14 xen01 kernel: ixgbe 0000:04:00.1 eth6: tx hang 1 
detected on queue 0, resetting adapter
Jan 17 23:40:14 xen01 kernel: ixgbe 0000:04:00.1 eth6: Reset adapter
Jan 17 23:40:15 xen01 kernel: ixgbe 0000:04:00.1 eth6: PCIe transaction 
pending bit also did not clear.
Jan 17 23:40:15 xen01 kernel: ixgbe 0000:04:00.1: master disable timed out
Jan 17 23:40:15 xen01 kernel: bonding: bond1: link status down for 
interface eth6, disabling it in 200 ms.
Jan 17 23:40:15 xen01 kernel: bonding: bond1: link status definitely 
down for interface eth6, disabling it
[...] repeated every second or so.

>> Are the devices connected to the same network infrastructure?
> 
> There are two onboard NICs and two NICs on a dual-port card in each
> server.  All devices connect to a cisco switch pair in VSS and the links
> are paired in LACP.

We've been experienced ixgbe stability issues on CentOS 6.x with various 
3.x kernels for years with different ixgbe driver versions and, to date, 
the only way to completely get rid of the issue was to switch from Intel 
to Broadcom. Just like in your case, the problem pops up randomly and 
the only reliable temporary fix is to reboot the affected Xen node. 
Another temporary fix that worked several times but not always was to 
migrate / shutdown the domUs, deactivate the volume groups, log out of 
all the iSCSI targets, "ifdown bond1" and "modprobe -r ixgbe" followed 
by "ifup bond1".

The set up is:
- Intel Dual 10Gb Ethernet - either X520-T2 or X540-T2
- Tried Xen kernels from both xen.crc.id.au and CentoS 6 Xen repos
- LACP bonding to connect to the NFS & iSCSI storage using Brocade 
VDX6740T fabric. MTU=9000

>> There has to be something common.
> 
> The NICs having issues are running a native VLAN, a tagged VLAN, iSCSI
> and NFS traffic, as well as some basic management stuff over SSH, and
> they are configured with an MTU of 9000 on the native VLAN.  It's a lot
> of features, but I can't really turn them off and then actually have
> enough load on the NICs to reproduce the issue.  Several of these
> servers were installed and being burned in for 3 months without ever
> having an issue, but suddenly collapsed when I tried to bring 20 or so
> real-world VMs up on them.

There "appears" to be some sort of load-dependent pattern here too, but 
it's impossible to confirm it.
The only stability improvement I was able to use "dom0_max_vcpus=1 
dom0_vcpus_pin". Haven't tried pci=nomsi yet.

> The other NICs in the system that are connected don't exhibit issues and
> run only VM network interfaces.  They are also in LACP and running VLAN
> tags, but normal 1500 MTU.
> 
> So far it seems to correlate with NICs on the expansion cards, but it's
> a coincidence that these cards are the ones with the storage and
> management traffic.  I'm trying to swap some of this load to the onboard
> NICs to see if the issues migrate over with it, or if they stay with the
> expansion cards.
> 
> If the issue exists on both NIC types, then it rules out the specific
> NIC chipset as the culprit.  It could point to the driver, but upgrading
> it to a newer version did not help and actually appeared to make
> everything worse.  This issue might actually be more to do with the PCIe
> bridge than the NICs, but these are still different motherboards with
> different PCIe bridges (5520 vs C600) experiencing the same issues.
> 
>> I've been using Intel NICs with Xen/CentOS for ages with no issues.
> 
> I figured that must be so.  Everyone uses Intel NICs.  If this was a
> common issue, it would probably be causing a lot of people a lot of trouble.
> 

Adi Pircalabu