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

[Avi Kivity <avi@qumranet.com>]

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


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