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Re: [Xen-devel] [PATCH RFC V4 4/5] kvm : pv-ticketlocks support for linux guests running on KVM hypervisor

On 01/18/2012 11:52 PM, Jeremy Fitzhardinge wrote:
> On 01/19/2012 12:54 AM, Srivatsa Vaddagiri wrote:
> >
> >> That logic relies on the "kick" being level triggered, so that "kick"
> >> before "block" will cause the block to fall out immediately.  If you're
> >> using "hlt" as the block and it has the usual edge-triggered behaviour,
> >> what stops a "kick-before-hlt" from losing the kick?
> > Hmm ..'hlt' should result in a check for kick request (in hypervisor
> > context) before vcpu is put to sleep. IOW vcpu1 that is attempting to kick 
> > vcpu0
> > will set a 'somebody_tried_kicking_vcpu0' flag, which hypervisor should 
> > check 
> > before it puts vcpu0 to sleep because of trapped 'hlt' instruction.
> >
> > Won't that trap the 'kick-before-hlt' case? What am I missing here?
> Nothing, that sounds fine.  It wasn't clear to me that your kick
> operation left persistent state, and so has a level-triggered effect on hlt.

btw, this persistent state needs to be saved/restored for live
migration.  Best to put it into some MSR.

error compiling committee.c: too many arguments to function

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