Re: [Xen-devel] Dom0 losing interrupts???

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 14.02.11 at 10:38, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> wrote:
> On 02/14/11 10:26, Jan Beulich wrote:
>>>>> On 14.02.11 at 07:59, Juergen Gross<juergen.gross@xxxxxxxxxxxxxx>  wrote:
>>> I used xen-unstable, kernel 2.6.32.24 from SLES11 SP1 on a 12 core INTEL
>>> nehalem machine. I pinned all 12 Dom0 vcpus to pcpu 1-2 and started a
>>> parallel
>>> build. After about 2 minutes the first missing interrupts were reported, a
>>> little bit later the next one, no xen messages are printed:
>>
>> That's certainly not too surprising, somewhat depending on the
>> maximally tolerated latencies. It seems unlikely to me for a 6-fold
>> CPU over-commit to promise stable operation, yet certain
>> adjustments could probably be done to make it work better (like
>> temporarily boosting the priority of a hardware interrupt's target
>> vCPU).
> 
> I would understand timeouts. But shouldn't the interrupt come in sooner or
> later? At least the megasas driver seems not to be able to recover from this
> problem, as a result my root filesystem is set to read-only...

I'm sure these interrupts arrive eventually, but the driver not
seeing them within an expected time window may still make it
report them as "lost".

> This would mean there is a problem in the megasas driver, correct?
> And Andre reports stability problems of his machine in similar cases, but
> in his case the network driver seems to be the reason.

Yes, this certainly depends on how the driver is implemented.

> Are you planning to prepare a patch for boosting the priority of vcpus being
> the target for a hardware interrupt? I think I would have to search some 
> time
> to find the correct places to change...

So far I had no plan to do so, and I too would have to do some
looking around. Nor am I convinced everyone would appreciate
such fiddling with priorities - I was merely suggesting that might
be one route to go. George?

Jan


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