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

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Message-ID: <20110304205512.GB2867@nik-comp.lan>
Date:	Fri, 4 Mar 2011 21:55:12 +0100
From:	Nikola Ciprich <extmaillist@...uxbox.cz>
To:	Glauber Costa <glommer@...hat.com>
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

> 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.



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