linux-kernel - Re: regression - 2.6.36 -> 2.6.37 - kvm

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Date:	Fri, 04 Mar 2011 16:09:22 -0300
From:	Glauber Costa <glommer@...hat.com>
To:	Nikola Ciprich <extmaillist@...uxbox.cz>
Cc:	Zachary Amsden <zamsden@...hat.com>, Avi Kivity <avi@...hat.com>,
	Nikola Ciprich <nikola.ciprich@...uxbox.cz>,
	KVM list <kvm@...r.kernel.org>,
	Linux kernel list <linux-kernel@...r.kernel.org>
Subject: Re: regression - 2.6.36 -> 2.6.37 - kvm - 32bit SMP guests don't
 boot

On Fri, 2011-03-04 at 19:27 +0100, Nikola Ciprich wrote:
> Hello Zachary,
> 
> > You don't see any messages about TSC being unstable or switching  
> > clocksource after loading the KVM module?  And you are not suspending  
> > the host or anything?
> no messages, no suspending, nothing.
> 
> 
> > Can you try using "processor.max_cstate=1" on the host as a kernel  
> > parameter and see if it makes a difference?
> I tried it, no change..
> n.

Zach,

I don't understand 100 % the logic behind all your tsc changes.
But kvm-clock-wise, most of the problems we had in the past were related
to the difference in resolution between the tsc and the host clocksource
(hpet, acpi_pm, etc), which in his case, it is a non-issue.

It does seem to me like some compensation logic kicked in, dismantling
an otherwise good tsc. He does have nonstop_tsc, which means it can't
get any better.

One thing I noticed when reading the culprit patch in bisect, is that in
vcpu_load(), there were previously a call to  

 kvm_request_guest_time_update(vcpu)

that was removed without a counterpart addition. Any idea about why it
was done?

Nikola, does adding that line back alleviate the problem for you ?

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