Re: What should be the interrupt period of a timer...

[Maynard J. <may...@us...>]

Groleo Marius wrote:
> Hi list,
> 
> I'm trying my luck with adding oprofile support for coldfire processors.
> So far I managed to come up with a oprofile.ko and a oprofile compiled
> for Coldfire. Since the CPU doesn't have performance counters, I used
> a programable Slice Timer.
> 
> The question I have is "what expire period
> should I set the Slice Timer to" ?
> 
oprofile is a statistical profiler, so the more frequent your samples are, the 
more statistically accurate they will be.  However, you'll find some point of 
diminishing returns, where the overhead of the kernel and userspace parts of 
oprofile are affecting overall system performance to the point of impacting the 
program you're profiling (or other users).  A rule of thumb or goal to shoot for 
is to keep the oprofile overhead to under 5% or so.  So just set the timer to 
some value and start collecting some profiles.  Examine how accurate they are 
and also look at how much oprofile overhead shows up in your profiles.  Adjust 
the timer accordingly and re-test.

-Maynard
[snip]