Re: a joint letter on low latency and Linux

[Benno Senoner]

Linus Torvals wrote:
> - I do think the "copy_to/from_user()" case is the cleaner one, but I'd
>   hate to do the test in-line, and I'd hate to do it all over the place.
>   And if we do it in copy_to/from_user(), we don't do it _anywhere_ else:
>   again the difference is one between a slightly tasteless hack, and a
>   ugly rule of life.

I may miss something, but Ingo's initial low latency patch, did just 
the schedule checks in the uaccess macros, but that was not enough to
cover all cases and ensure flat latency diagrams under all kinds of load.

So I am curious if the "we don't do it anywhere else" thing is possible
in practice, without requiring a radical change within the kernel. 

Question: From a pure overhead point of view: does the preemption-points
approach score better (how much) than other approaches (eg pre-emptable kernel)
? 

Benno.