Re: [patch] Real-Time Preemption, -VP-2.6.9-rc4-mm1-U1

[Timothy Miller <miller@techsource.com>]

Mark_H_Johnson@raytheon.com wrote:

> 
> In the systems I have to deal with, I do not have a clear criteria
> to set priorities of interrupts relative to each other. For example, I
> have a real time simulation system using the following devices:
>  - occasional disk access to simulate disk I/O
>  - real time network traffic
>  - real time delivery of interrupts from a PCI timer card and APIC timers
>  - real time interrupts from a shared memory interface
> The priorities of real time tasks are basically assigned based on the
> rate of execution. 80 Hz tasks run at a higher priority than 60 Hz, 60 Hz >
> 40 Hz, and so on. A number of tasks can access each device.
> 


What if drivers could indicate how much "jitter" (essentially, latency) 
its interrupts can tolerate?  Higher jitter would SORTOF translate into 
lower priority, although the scheduler would make sure the IRQ was 
started before its tolerance ran out (ie. the priority approaches 
infinity as its tolerance period approaches the end).  The jitter 
tolerance would be measured in microseconds, I guess.