Re: [PATCH 03/15] kvm: Install optimized interrupt handlers

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-03-06 03:13, Marcelo Tosatti wrote:
> On Sat, Mar 05, 2011 at 07:11:53PM +0100, Jan Kiszka wrote:
>> On 2011-03-05 16:37, Marcelo Tosatti wrote:
>>> On Fri, Mar 04, 2011 at 11:20:00AM +0100, Jan Kiszka wrote:
>>>> KVM only requires to set the raised IRQ in CPUState and, if the user
>>>> space irqchip is used, to kick the receiving vcpu if it is remote.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>> ---
>>>>  kvm-all.c |   17 +++++++++++++++++
>>>>  1 files changed, 17 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/kvm-all.c b/kvm-all.c
>>>> index 226843c..c460d45 100644
>>>> --- a/kvm-all.c
>>>> +++ b/kvm-all.c
>>>> @@ -650,6 +650,20 @@ static CPUPhysMemoryClient kvm_cpu_phys_memory_client = {
>>>>      .log_stop = kvm_log_stop,
>>>>  };
>>>>  
>>>> +static void kvm_handle_interrupt(CPUState *env, int mask)
>>>> +{
>>>> +    env->interrupt_request |= mask;
>>>> +
>>>
>>> If the env->interrupt_request request is processed in userspace, such as
>>> MCE, the kick is still necessary for irqchip case. CPU_INTERRUPT_DEBUG
>>> is another example, no?
>>
>> [this probably targeted kvm_handle_interrupt_kernel_irqchip]
>>
>> In principle, you are right. But MCE must be injected synchronously over
>> the target VCPU, see do_inject_x86_mce, and CPU_INTERRUPT_DEBUG is also
>> synchronous and not even used in KVM mode.
> 
> CPU_INTERRUPT_NMI from monitor?
> 
> Don't see what gain you expect from avoiding the signal in this case.

Well, looking at this from a different angle again, I cannot identify my
original optimization anymore. I guess I was under the wrong impression
that cpu_interrupt is still a frequently used service even with
in-kernel irqchip. But that's by far not the case.

Will drop this.

Jan


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