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

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Message-ID: <20111214182101.GB21945@amt.cnet>
Date:	Wed, 14 Dec 2011 16:21:01 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Eric B Munson <emunson@...bm.net>, mingo@...hat.com, hpa@...or.com,
	arnd@...db.de, ryanh@...ux.vnet.ibm.com, aliguori@...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 Wed, Dec 14, 2011 at 04:39:56PM +0200, 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.

Slow enough that progress of the watchdog thread is unable to keep up
with timer interrupt processing. This is considered a hang and
should be reported.

> > About SIGSTOP, that is a corner case. Unsure if its even properly supported 
> > by QEMU.
> 
> It works from my experience.


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