> I'd like to time some funcs implemented in an extension but they are
> really fast so:
> 
> start = Time.now
> my_ext_function(args)
> elapsed_time = Time.now - start
> 
> will not do (resolution is microsecs?). 

Some help might be at the
http://dev.rubycentral.com/ref/ref_c_time.html#usec

And my ruby-cygwin run this (shamelessly ripped from excellent reference):

  ruby -e "t=Time.now; puts ('%10.6f' % t.to_f); puts t.usec;"

and outputs this:
964445231.186000
186000

> (Platform-specific syscalls not allowed!)

This has to be quite platform specific, AFAIK C standards do not impose
requirements for better resolution than second. So my guess, without look to
sources, is that microseconds are not supported on all platforms (and
relying on them is not good idea anyway).

	- Aleksi