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

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Date:	Thu, 15 Dec 2011 13:53:46 -0500
From:	Eric B Munson <emunson@...bm.net>
To:	Avi Kivity <avi@...hat.com>
Cc:	mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com, mtosatti@...hat.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 Thu, 15 Dec 2011, Avi Kivity wrote:

> On 12/14/2011 07:58 PM, Eric B Munson wrote:
> > > I don't think you should see a guest softlockup if the host is
> > > overloaded.  Nor should you see it due to a long live migration pause,
> > > or STOP/CONT.  You should see a guest softlockup if it is spinning due
> > > to a guest bug, and not for any other reason.
> > > 
> > > I think we need a mix of the ioctl (for STOP/CONT and voluntary pauses,
> > > like live migration or qemu stop/cont) and preempt notifiers (together
> > > with a check for TASK_RUNNING/TASK_UNINTERRUPTIBLE, for scheduling or
> > > swap delays)
> > > 
> >
> > Do you want the preemption notifier work in before you will consider merging
> > this set, or can that be a follow on?
> 
> Yes please.
> 
> -- 
> error compiling committee.c: too many arguments to function
> 

I am working on V7 to incorporate the __this_cpu_and suggestion, would you
consider that for inclusion and we can continue discussing the need for the
preemption notification work?  I think that having a guest complain when the
host is so loaded that the guest watchdog threads can't make any progress is
desirable behavior, it may be the only notification that an admin gets that a
particular host is over loaded.

Eric

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