Re: Questions about GPLPV stability tests

[Andreas Kinzler <ml-xen-devel@hfp.de>]

>> Not in this year of my stability tests. In this year I am always
>> experiencing crashes of domU only. dom0 was always stable.
>> But last year, I hunted a very serious problem which causes nasty
>> hangs/crashes in dom0 (which crashes domU as a consequence). See this
>> mailing list post:
>> http://lists.xen.org/archives/html/xen-devel/2010-09/msg00556.html
>> In my tests it clearly shows that if you have a CPU without ARAT and you
>> don't have the patch from my post, your Xen 4.0.1 or 4.1.1 will crash under
>> load and/or after a while. What is your CPU?
> Most of our machines use i7 950 CPUs. They don't seem to have ARAT.

Yes, i7 950 does not have ARAT as it is the first Nehalem generation.

> Some other machines use Xeon CPUs with ARAT support. We never had
> issues on the Xeon systems, so we may actually be suffering from the
> ARAT issue. Are you still using the patch you linked to in a
> production environment?

Absolutely. As I mentioned I just re-performed tests recently and found 
that even Xen 4.1.1 (earlier tests were for 4.0.1) is unstable without 
my patch on non-ARAT-CPUs.

 > I wonder why a cleaned up patch like that never made it into core.

The patch actually only disables HPET broadcast which has some downsides 
because it effectively disables C3 states. Without C3 states Nehalem and 
later CPUs cannot enter turbo-mode. So there is some loss of performance.

> I'm going to do some testing (may take a while).

Please let me know. There are already some people confirming that HPET 
broadcast is buggy. With more evidence I will contact Keir again and 
suggest to have it (HPET broadcast) fixed or removed.

Regards Andreas