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

[Jan Kiszka]

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.

Jan

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