Re: [PATCH 6/6 V2] Add age out of guest paused flag

[Anthony Liguori]

On 11/01/2011 02:51 PM, Eric B Munson wrote:
> On Tue, 01 Nov 2011, Anthony Liguori wrote:
>
> > On 10/31/2011 03:07 PM, Eric B Munson wrote:
> > > The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft
> > > lockup but it can mask real soft lockups if the flag isn't cleared when it is
> > > no longer relevant.  This patch adds a kvm ioctl that the hypervisor will use
> > > when it resumes a guest to start a timer for aging out the flag.  The time out
> > > will be specified by the hypervisor in the ioctl call.
> > >
> > > Signed-off-by: Eric B Munson<emunson@xxxxxxxxx>
> >
> > Why not have the guest clear the flag when it acknowledges it?
> >
> > The hypervisor would unconditionally set the bit, and the guest
> > would do a testandclear to check if the bit is set.  I think that
> > avoids the whole aging business.
> >
> > Regards,
> >
> > Anthony Liguori
>
> If you have a look at patch 5 of this series, the flag is cleared when the
> guest checks the validity of a soft lockup.  However, the aging is meant to
> cover the case where the guest never sees a soft lockup.  We don't want this
> flag to be stored for ever and end up delaying real soft lockup messages.  With
> that case in mind, I thought this was a good/simple compramise.

If the guest clears the flag, then I don't think you have to worry about this.

Regards,

Anthony Liguori

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