linux-kernel - Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host

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Message-ID: <4EE8B78F.9090104@us.ibm.com>
Date:	Wed, 14 Dec 2011 08:49:51 -0600
From:	Anthony Liguori <aliguori@...ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Eric B Munson <emunson@...bm.net>, mingo@...hat.com,
	hpa@...or.com, arnd@...db.de, ryanh@...ux.vnet.ibm.com,
	jeremy.fitzhardinge@...rix.com, levinsasha928@...il.com,
	Jan Kiszka <jan.kiszka@...mens.com>, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped
 by host

On 12/14/2011 08:39 AM, Avi Kivity wrote:
> On 12/14/2011 02:16 PM, Marcelo Tosatti wrote:
>>> Having this controlled from userspace means it doesn't work for SIGSTOP
>>> or for long scheduling delays.  What about doing this automatically
>>> based on preempt notifiers?
>>
>> Long scheduling delays should be considered hangups from the guest
>> perspective.
>
> Why?  To the guest it looks like slow hardware, but it will interpret it
> as a softlockup.
>
>> About SIGSTOP, that is a corner case. Unsure if its even properly supported
>> by QEMU.
>
> It works from my experience.

We don't adjust vm_clock's offset on SIGSTOP/SIGCONT so while it may appear to 
work okay, QEMU isn't exhibiting the behavior it is supposed to.

Regards,

Anthony Liguori

>

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