Portability	non-portable (requires IA-32 processor and GHC)
Stability	provisional
Maintainer	magr@cs.tu-berlin.de

System.CPUTime.Rdtsc

Description

This module provides the function rdtsc for accessing the rdtsc machine register on modern IA-32 processors. This is a 64-bit counter which counts the number of processor cycles since the machine has been powered up.

As an example, you may use the following program to measure the overhead of calling this function:

 module Main where
 import System.CPUTime.Rdtsc

 main = do
   t1 <- rdtsc
   t2 <- rdtsc
   putStrLn ("Cost of rdtsc (ffi call):    " ++ show (t2 - t1))

Synopsis

Documentation

rdtsc :: IO Word64 Source

Return the number of clock cycles since the machine this function is called on has been powered up. Note that the value returned may be inaccurate if the program is run on some hardware virtualization layer.

Especially on multi-core processors and when using hibernating operating systems, the values returned may be bogus.

For more information about the rdtsc instruction, see http://en.wikipedia.org/wiki/RDTSC