Re: megasas stops I/O when running kernel as dom0 under xen4.1/4.2

[Keir Fraser <keir.xen@gmail.com>]

On 30/08/2011 13:11, "Andrew Cooper" <andrew.cooper3@citrix.com> wrote:

> On 30/08/11 13:02, Andreas Olsowski wrote:
>> --snip--
>>> Apologies - previous patch fails to compile (i forgot to hg qrefresh
>>> before sending - it has been a very long day).  Try this patch.
>> Testing right now, so far it seems to do fine, patching worked, so did
>> compilation.
>> 
>> A scenario that previously stopped io does no longer stop it.
>> 
>> Ill give it a couple of more tries and days, but it sure looks good.
>> 
>> Any chance of introducing this patch into xen-4.1-testing and making
>> it a part of the upcoming xen-4.1.2?
>> 
>> 
>> with best regards,
>> 
>> Andreas
>> 
> 
> That is up to Keir.  My opinion is that this patch is more of a hack
> than a solution, especially as it does involve changing the API for
> interrupt ops, but that does not necessarily prevent it from being included.

I think this is the right sort of minimal, focused fix that is appropriate
for our stable branch, just as it is appropriate for a product patch queue.

> I will soon be working on some significant changes to the interrupt code
> (cleanup of structures, cleanup of logic - specifically the logic which
> is now false with per-cpu IDTs) with an intension to upstream them, but
> whether these patches are suitable to backport is an entirely different
> question.

Yes, it's questionable, it's definitely not going to be ready let alone
tested in time for 4.1.2.

Please post your hacky fix against 4.1-testing with signed-off-by line. I
think we should go with it, much preferable to releasing 4.1.2 with a known
bug of this type left unfixed. Possibly it is appropriate for 4.0.3 as well?
It has the per-cpu idt logic as well.

 Thanks,
 Keir

> 
> On a completely different note, we have got in contact with LSI who are
> altering their driver to consider MSI interrupts as well as MSI-X
> interrupts, which will be sensible to take, as MSI interrupts will give
> you an order of magnitude faster disk IO, irrespective of the line level
> bug in Xen.
> 
> ~Andrew