Re: [Xen-devel] [Xen-users] Network and SATA Instability on Xen 4.6/4.8

["Jan Beulich" <JBeulich@xxxxxxxx>]

(dropping xen-users, to avoid cross posting)

>>> On 20.12.17 at 18:40, <dunlapg@xxxxxxxxx> wrote:
> On Fri, Dec 8, 2017 at 9:17 PM, Kevin Stange <kevin@xxxxxxxxxxxxx> wrote:
>> Hi,
>>
>> I've been running Xen 4.4 stably for some time under kernel 4.9 in dom0
>> on CentOS 6 and have been trying to finally move my environment up to
>> Xen 4.6 or 4.8 using CentOS 7.  Since I've built out my test server with
>> Xen 4.6, I've been having issues where the Intel NICs begin flapping
>> repeatedly and the SATA disk interfaces go down and will not come back
>> up until I reboot the server.  Even sending the bus rescan command
>> doesn't bring the drives back.  The issue seems to trigger based on
>> activity, so during something like an mdraid resync is more likely to
>> cause the issue, but it's not reproducible in a consistent amount of
>> time, which makes it hard to tell if a particular change has definitely
>> fixed it.
>>
>> This is reminiscent of a problem I had been experiencing while running
>> kernel 3.18 and Xen 4.4 on CentOS 6, but the problem resolved itself
>> upon upgrading to kernel 4.4 and later 4.9, so I chalked that up to
>> something bad with PCIe management in kernel 3.18 and thought nothing
>> more of it until now.
>>
>> The initial test environment where the issue occurred was kernel 4.9.58
>> and Xen 4.6.6-7 (with security patches from CentOS).  I then tried
>> upgrading to kernel 4.9.63 and Xen 4.8.2-5, which didn't result in any
>> improvements.
>>
>> I tried pcie_aspm=off on the kernel line, which has helped in the past
>> with similar issues, but that didn't help here.
>>
>> I tried booting without Xen (just kernel 4.9.63) and it seems like that
>> made the issue go away, which lead me to believe the issue only happens
>> with hardware accessed from dom0.  I dug through Xen command line
>> options and tried booting with msi=off and that now seems to have
>> resulted in the problem going away, or at least, the system hasn't
>> exhibited the issue since last week.  Previously, the issue would tend
>> to manifest after less than 24 hours.
>>
>> My hardware is Supermicro X8DT3-F with Dual Intel Xeon E5620 CPUs.
>>
>> Disk issues begin with a kernel message like this followed by continuous
>> ATA command failures:
>>
>> ata2.00: exception emask 0x0 sact 0x7c01ffff serr 0x50000 action 0x6 frozen
>>
>> NIC issues begin with a message like:
>>
>> igb 0000:04:00.1: enp4s0f1: Reset adapter unexpectedly
>>
>> NICs do recover almost immediately but continue to flap periodically
>> until reboot.
>>
>> I don't know if this is a bug in Xen or something else at play, but I
>> could really use some help figuring out what's going on, why msi=off
>> seems to fix it, and if there are any better ways to resolve this.
> 
> Jan / Andy,
> 
> Any idea why Kevin might be seeing stability issues under 4.6 / 4.8
> that is solved by adding 'msi=off'?

Nothing I've ever heard of, and without at least full logs also very
difficult to consider possible options. While I don't recall any
significant bug fixes in this area since 4.8, trying with 4.10 (and
perhaps also a more up-to-date Dom0 kernel) would certainly be
worthwhile. With the information at hand it's not even possible
to tell whether Xen or the Dom0 kernel is the problematic part
here (the fact that Linux works fine natively doesn't mean much
here, as MSI handling is quite a bit different when running on
Xen).

What I suspect first of all is that some interrupt is not making it
through to its handler. It may be possible to see something from
debug key output ('M' and 'i') once the system is in that state.

Just to be sure - use of an IOMMU does not affect the behavior?

Jan


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