> -----Original Message-----
> From: [email protected] [mailto:kvm-ppc-
> [email protected]] On Behalf Of Alexander Graf
> Sent: Tuesday, September 27, 2011 1:45 PM
> To: Wood Scott-B07421
> Cc: Liu Yu-B13201; Wood Scott-B07421; [email protected]
> Subject: Re: [PATCH 5/5] KVM: PPC: booke: Improve timer register
> emulation
>
>
> On 27.09.2011, at 02:44, Scott Wood wrote:
>
> > On 09/24/2011 02:27 AM, Alexander Graf wrote:
> >> I think I'm getting your point. So what we want is:
> >>
> >> in timer handler:
> >>
> >> set_bit(TSR_DIS, vcpu->arch.tsr);
> >> kvm_make_request(KVM_REQ_PPC_TSR_UPDATE, vcpu);
> >> kvm_vcpu_kick(vcpu);
Still there can be a case where first request not handled and another event
happens? Or we would like to pause till first request is handled by vcpu?
Thanks
-Bharat
> >>
> >> in vcpu entry code:
> >>
> >> if (vcpu->requests)
> >> if (kvm_check_request(KVM_REQ_PPC_TSR_UPDATE, vcpu))
> >> kvmppc_update_tsr(vcpu);
> >>
> >> void kvmppc_update_tsr(struct kvm_vcpu *vcpu) {
> >> if (vcpu->arch.tsr & TSR_DIS &&
> >> vcpu->arch.tcr & TCR_DIE) {
> >> kvmppc_core_queue_dec(vcpu);
> >> }
> >> // XXX also implement dequeue!
> >> }
> >
> > OK, this avoids the possibility for the guest to clear DIS/DIE after
> > enqueue but before delivery (which in the current patch is dealt with
> > by an extra check at delivery), and we only have to check one thing in
> > the common nothing-requested case (even if more things use this
> > mechanism, as long as we don't run out of bits).
> >
> > If we convert external IRQs to using this as well, and expand the
> > timer case to include non-booke (maybe just use
> > KVM_REQ_PENDING_TIMER?), we should be able to de-atomicize
> > pending_exceptions (which should be a bigger win than de-atomicizing
> arch.tsr).
> >
> >> case SPR_TSR:
> >> vcpu->arch.tsr &= ~TSR_DIS;
> >> kvmppc_update_tsr(vcpu);
> >
> > Well, we should probably replace TSR_DIS here with the actual value
> > that the guest wrote. :-)
>
> Yes, and use the atomic operation. This is all just pseudo-code.
>
> I like the idea of moving pending_exceptions off of atomic. This really
> is a private field that no other vcpu should have access to. We only have
> to think hard about how to implement SET_INTERRUPT for another vcpu then.
> But I think this could just be another kvm_make_request() type.
>
>
> Alex
>
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