[Qemu-devel] Re: [PATCH 17/22] kvm: Move irqchip event processing out of inner loop

[Gleb Natapov]

On Mon, Jan 31, 2011 at 05:52:13PM +0100, Jan Kiszka wrote:
> On 2011-01-31 17:50, Gleb Natapov wrote:
> > On Mon, Jan 31, 2011 at 05:41:24PM +0100, Jan Kiszka wrote:
> >> On 2011-01-31 17:38, Gleb Natapov wrote:
> >>> On Mon, Jan 31, 2011 at 04:40:34PM +0100, Jan Kiszka wrote:
> >>>> On 2011-01-31 14:04, Jan Kiszka wrote:
> >>>>> On 2011-01-31 12:36, Jan Kiszka wrote:
> >>>>>> On 2011-01-31 11:08, Avi Kivity wrote:
> >>>>>>> On 01/27/2011 03:10 PM, Jan Kiszka wrote:
> >>>>>>>> Align with qemu-kvm and prepare for IO exit fix: There is no need to 
> >>>>>>>> run
> >>>>>>>> kvm_arch_process_irqchip_events in the inner VCPU loop. Any state 
> >>>>>>>> change
> >>>>>>>> this service processes will first cause an exit from kvm_cpu_exec
> >>>>>>>> anyway. And we will have to reenter the kernel on IO exits
> >>>>>>>> unconditionally, something that the current logic prevents.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Jan Kiszka<address@hidden>
> >>>>>>>> ---
> >>>>>>>>   kvm-all.c |   11 ++++++-----
> >>>>>>>>   1 files changed, 6 insertions(+), 5 deletions(-)
> >>>>>>>>
> >>>>>>>> diff --git a/kvm-all.c b/kvm-all.c
> >>>>>>>> index 5bfa8c0..46ecc1c 100644
> >>>>>>>> --- a/kvm-all.c
> >>>>>>>> +++ b/kvm-all.c
> >>>>>>>> @@ -892,6 +892,12 @@ int kvm_cpu_exec(CPUState *env)
> >>>>>>>>
> >>>>>>>>       DPRINTF("kvm_cpu_exec()\n");
> >>>>>>>>
> >>>>>>>> +    if (kvm_arch_process_irqchip_events(env)) {
> >>>>>>>> +        env->exit_request = 0;
> >>>>>>>> +        env->exception_index = EXCP_HLT;
> >>>>>>>> +        return 0;
> >>>>>>>> +    }
> >>>>>>>> +
> >>>>>>>>       do {
> >>>>>>>>   #ifndef CONFIG_IOTHREAD
> >>>>>>>>           if (env->exit_request) {
> >>>>>>>> @@ -901,11 +907,6 @@ int kvm_cpu_exec(CPUState *env)
> >>>>>>>>           }
> >>>>>>>
> >>>>>>> We check for ->exit_request here
> >>>>>>>
> >>>>>>>>   #endif
> >>>>>>>>
> >>>>>>>> -        if (kvm_arch_process_irqchip_events(env)) {
> >>>>>>>> -            ret = 0;
> >>>>>>>> -            break;
> >>>>>>>> -        }
> >>>>>>>> -
> >>>>>>>
> >>>>>>> But this checks for ->interrupt_request.  What ensures that we exit 
> >>>>>>> when 
> >>>>>>> ->interrupt_request is set?
> >>>>>>
> >>>>>> Good question, need to check again. But if that turns out to be an
> >>>>>> issue, qemu-kvm would be broken as well. I'm just aligning the code 
> >>>>>> here.
> >>>>>>
> >>>>>
> >>>>> The only thing we miss by moving process_irqchip_events is a self-INIT
> >>>>> of an AP - if such thing exists in real life. In that case, the AP would
> >>>>> cause a reset of itself, followed by a transition to HALT state.
> >>>>
> >>>> I checked again with the Intel spec, and a self-INIT is invalid (at
> >>>> least when specified via shorthand). So I'm under the impression now
> >>>> that we can safely ignore this case and leave the patch as is.
> >>>>
> >>>> Any different views?
> >>>>
> >>> IIRC if you don't use shorthand you can send INIT to self.
> >>
> >> We didn't care so far (in qemu-kvm), do you think we should?
> >>
> > Doesn't kernel lapic emulation support this?
> 
> See the my other mail: It supports it, but it apparently doesn't expects
> this to happen.
> 
I saw it, but I do not understand why do we print this message. May be
it was used for debugging in early stages of KVM development.

--
                        Gleb.