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Re: [Xen-devel] megasas stops I/O when running kernel as dom0 under xen4.1/4.2

On 24/08/11 18:20, Andrew Cooper wrote:
> On 24/08/11 18:09, Konrad Rzeszutek Wilk wrote:
>> On Wed, Aug 24, 2011 at 05:57:06PM +0100, Andrew Cooper wrote:
>>> On 24/08/11 13:06, Andrew Cooper wrote:
>>>> On 22/08/11 10:05, Andrew Cooper wrote:
>>>>> On 19/08/11 19:10, Andreas Olsowski wrote:
>>>>>> Am 19.08.2011 18:49, schrieb Andrew Cooper:
>>>>>>> The only change you need to make is in megasas_probe_one() in
>>>>>>> megaraid_sas_base.c
>>>>>>> Add a call to pci_enable_msi(pdev) immediately after the current
>>>>>> call to
>>>>>>> pci_set_master(pdev);
>>>>>>> ~Andrew
>>>>>> Yep, that works fine. Removed the module option as well.
>>>>>> root@tarballerina:~# cat /proc/interrupts  |grep mega
>>>>>> 2236:      69010          0          0          0          0         
>>>>>> 0          0          0  xen-pirq-msi       megasas
>>>>>> The same procedure that would have lead to almost instant errors has
>>>>>> not brought them to appear again.
>>>>> Good.  This is what we are seeing as well.  I am still awaiting a reply
>>>>> from LSI on this topic.
>>>>> Unfortunately, this does point to a regression in the way Xen deals with
>>>>> legacy interrupts.
>>>> Out of interest, on all 3 of your boxes with the megaraid_sas cards,
>>>> could you gather the io_apic information?
>>>> It is the z xen debug key on the serial console (or alternatively put
>>>> apic_verbosity=debug on the xen commandline and the information gets
>>>> dumped into the dmesg)
>>> You can ignore this - it is not relevant.
>>> I have narrowed the problem to a bug in the interrupt migration code.
>> Goodies!
>>> The bug occurs when the move pending flag is set, and somehow another
>>> interrupt comes in on the old pcpu without triggering the move
>>> completion code.  This leaves the IO_APIC with ack'd but not EOI'd
>>> interrupt from the megaraid_sas device.
>> Ah, so the interrupt is delievered to Dom0 on the old per_cpu
>> event which is ignored. Ignored b/c we have rebinded the event channel
>> to the other CPU, right?
> The interrupt is not ignored - it seems to be being serviced by the
> device driver in dom0.   I will admit that my debugging code may be a
> bit flaky - I started by trying to match IRQ35 (which is always claimed
> by PCI INTA on this server - very useful for debugging) between do_IRQ
> and its related PHYSDEVOP_eoi.
> I am currently trying to track the exact order of events around this
> interrupt which misses the move completion code.
>> Is there any code in the Hypervisor to turn off interrupt migration code?
> Not that I have found, although playing around with vcpu and task
> pinning should work.  My debugging shows that Xen-4.1.1 is migrating
> this interrupt between PCPUs on average once every 4 real interrupts
> when dom0 is under any load whatsoever.

Please try attached patch.  It is a hack, but it works as far as I can test.

(Patch is taken against xen-4.1.1 but should be trivial to port if it
doesn't apply cleanly)


Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com

Attachment: debug-wip.patch
Description: Text Data

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