Re: [User-mode-linux-devel] IRQ handling

[Jeff D. <jd...@ka...>]

jl...@mi... said:
> I would like to propose adding interrupt handling to the UM kernel.

Are you volunteering to do it, or just saying it would be a good thing?

> [ much snippage with which I agree ]

> Any comments? 

Yeah.  I never said that interrupts were never going to happen.  They're just 
something I haven't gotten around to yet.  I add stuff when I miss it.  And I 
don't really miss real interrupts.  The timer handles everything.  That hurts 
latency, since the timer only happens every 50ms, but you don't really notice 
that too much.

That being said, my thinking on interrupts is that we should probably use 
SIGIO as the hardware interrupt.  I think there are some subtleties on where 
SIGIO gets delivered.  You'd have to make sure that it gets delivered to the 
process that's currently running and not to a stopped process.  There's also a 
race to be careful of when input happens as a context switch is happening.  
You need to make sure that SIGIO doesn't get delivered to a process that has 
just been stopped.  I don't think that's a big deal, you just need to be a 
little careful.

With SMP, we'd need to find a mechanism to round-robin the interrupts around 
to the different running processes.  I have no idea how that would work.

I don't think there's any magic here.  It might not even be that hard to do.  

				Jeff