Re: [RFC] QEMU/KVM: dedicated IO thread

Avi Kivity
2008-03-26T16:57:04Z

Marcelo Tosatti wrote:
>
>>> QEMU/KVM: separate thread for IO handling
>>>
>>> Move IO processing from vcpu0 to a dedicated thread.
>>>
>>> This removes load on vcpu0 by allowing better cache locality and also
>>> improves latency.
>>>
>>> We can now block signal handling for IO events, so sigtimedwait won't
>>> race with handlers:
>>>
>>> - Currently the SIGALRM handler fails to set CPU_INTERRUPT_EXIT because
>>> the "next_cpu" variable is not initialized in the KVM path, meaning that
>>> processing of timer expiration might be delayed until the next vcpu0 exit.
>>>
>>>
>> I think we call main_loop_wait() is called unconditionally after every
>> signal.
>>
>
> We exit the kvm_run() loop if CPU_INTERRUPT_EXIT is detected by pre_kvm_run().
>
>

But why do we need to exit the kvm_run() loop? As I understand it, the
I/O thread wakes up when the signal is queued and calls main_loop_wait()
to process any events (through qemu_run_timers()). If a timer needs to
wake up a vcpu, it will raise an interrupt line which will wake the vcpu
up, either in the kernel or in userspace depending on -no-kvm-irqchip.

--
error compiling committee.c: too many arguments to function