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

[Jan Kiszka <jan.kiszka@siemens.com>]

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<jan.kiszka@siemens.com>
>>>>>> ---
>>>>>>   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?

Jan

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