On 1/2/07, Martin Grabmueller wrote:
version 1.0 of package rdtsc has just been released. This small package contains one module called 'Rdtsc.Rdtsc'. This module provides the function 'rdtsc' for accessing the 'rdtsc' machine register on modern IA-32 processors.
Very nice! I have a few comments: 1. What happens when someone tries this on a platform other than IA-32? I would hope for some predictable exception to be thrown (hopefully not a segfault). Hmm, checking System.Info.arch would probably cost a few cycles. I wonder how much difference that would make. Or maybe there is a CPP macro that could hide this function completely on non-IA-32? 2. Shouldn't this module be called System.Rtdsc? Or maybe even System.CPUTime.Rdtsc (even though to a systems person this is a very different animal, something feels right about that to me. I think that is where most people would look for it first.).
...note that you can get strange results sometimes on a superscalar processor.
There are a number of serious problems with using RDTSC, so anyone using it should first read up about it. In particular: using it on a very old machine could prevent Linux from booting; using it on recent high-end machines can be very inaccurate (as Martin pointed out). Microsoft "strongly discourages" its use on Windows. That said, in practice many people find RDTSC very useful. Source: http://en.wikipedia.org/wiki/RDTSC Thanks for posting this module. Regards, Yitz _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
