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

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Date:	Fri, 04 Mar 2011 18:41:46 -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 21:55 +0100, Nikola Ciprich wrote:
> > 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 ?
> Hello Glauber,
> kvm_request_guest_time_update seems to have been renamed and then
> removed since then, but I've added 
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> instead and now the guest boots!
> So maybe missing clock update is really the culprit here?
> What do You guys think?
> n.

I think although the long term plan is to just do this update once in
your case (stable tsc), this update is needed. 

Why don't you send a patch to re-include it ?

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