[Open-graphics] Video interrupt enable/disable

[Timothy Normand Miller]

On 4/19/07, James Richard Tyrer <tyrerj at acm.org> wrote:

> At first look, it appears to me that the service ISR could cause latency
> problems with the sync interrupt if they share the same interrupt.  This
> is the real issue that needs to be discussed.

You are right about that.  But I don't see how _we_ can fix it.  This
is the domain of OS experts, like the people on LKML.

Besides, I have a tendency to want to design things so that latency is
not an issue.  For instance, we want to save on CPU overhead by
putting a GPU-using process to sleep after it's queued up a bunch of
requests.  We need to wake it up at some point to have it continue.
The solution is to design it so that the interrupt comes when the GPU
is still busy but nearing the end of being busy so that the producer
of commands can start producing them again before the last batch is
finished being processed.  This way, the GPU stays busy constantly,
regardless of the latency on interrupts or, far far worse, the time
required to wake the user process back up again.

Hanging 50 IRS off of one interrupt line is bad.  But I think we're
going to encounter other problems that make that pale in comparison.


-- 
Timothy Normand Miller
http://www.cse.ohio-state.edu/~millerti
Open Graphics Project