Re: gettimeofday is at the end of its usefulness?

On Thu, May 15, 2014 at 8:19 AM, Benedikt Grundmann
<bgrundmann@janestreet.com> wrote:
> I posted this on this mailing list before at Jane Street we have developed
> very fast code to get timing information based on TSC if available.  It's
> all ocaml but well documented and mostly just calls to c functions so should
> be easy to port to C and we release it under a very liberal license so it
> should be no problem to take the ideas:

What OS do you run it on though? How fast is your implementation
compared to the kernel implementation of clock_gettime()?

Are you sure your implementation is actually faster? And are you sure
you're protected against clocks going backwards? I think you should
put some i/o in the loop in the test and start several threads running
it to make it more likely the thread is rescheduled to a different
processor during the test. It suspect you'll find the rdtsc goes
backwards sometimes or produces crazy results when switching
processors.

-- 
greg