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

[Jan Kiszka]

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.

A self-SIPI has no effect as A) a CPU can't send a SIPI from
wait-on-SIPI state and B) SIPIs are ignored in any other state.

Will post a version that additionally checks for pending INIT as well
and injects a self-ipi then.

Jan

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