Re: assign-dev: Purpose of interrupt_work

[Avi Kivity <avi@redhat.com>]

On 10/12/2009 11:25 AM, Jan Kiszka wrote:
>>> Or what is the
>>> alternative?
>>>
>>>        
>> irqfd (which only supports edge-triggered interrupts now).  Note irqfd
>> needs the same love, it uses a workqueue as well.
>>
>> The theory is:
>>   fd1 = eventfd()
>>   give fd1 to kvm as irqfd, vhost-net as trigger fd
>>   fd2 = eventfd()
>>   give fd2 to kvm as irqfd, uio as trigger fd
>>   fd3 = evenfd()
>>   give fd3 to kvm as irqfd, another kvm as ioeventfd
>>
>> One interface, multiple users (in the kernel, userspace, or other
>> processes)
>>      
> I see to overall gain, but likely only worsens my objective (low
> latency), at least it doesn't improve it.
>    

irqfd can work from interrupt context, so if we only use the workqueue 
for the many-vcpu cases, we should be fine.

I think we can do it cleanly, too: in ioapic code, if we're talking to 
one vcpu, wake it immediately; otherwise schedule work to continue in 
process context.  This was the common code can always work in interrupt 
context and not worry about the work queue.

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