Re: Doubt: Does RT patch reduce interrupt latency?

[Stefan Agner <stefan.agner@yahoo.com>]

Hi,



> Thank you for this clarification. This really made me think. In
> mainline kernel, my interrupt will not be affected by other processes.
> But, it can be affected by other interrupts in the system, right? So,
> I still gain something from rt patch where I can scale down the
> priority of other interrupts so that they don't come in the way of my
> 1 ms interrupt.
Yes this is correct...

> Now, if I got it correct, what I will have to see is whether this
> advantage outweighs the disadvantage of context switching delays. A
> quick search showed me http://choices.cs.uiuc.edu/ExpCS07.pdf. In page
> 25 they have listed time for context switches and interrupts. Those
> figures are rather dismal (~few milli seconds). Can someone familiar
> with ARM here tell me whether these numbers can be trusted? From the
> rt wiki I see that, on ARM, worst case latency is less than 300us. I
> will anyway repeat the tests that we did so far and will post the
> results again.
I did such messures in my diploma work, its written in german but you should 
be able to read the figures (the messures are done on an arm cpu):
http://www.agner.ch/linuxrealtime/Linux-Realtime-Faehigkeiten.pdf

PDF Page 47 and following are interessting. You can see the 
"Durchschnittslatenzzeiten" (average latencies) rt compared with mainline

Bye
Stefan