On Mon, Apr 21, 2008 at 07:54:24PM +0100, Andrew Coppin wrote: > Jim Snow wrote: >> Useful references: "What Every Programmer Needs to Know About Memory" >> http://lwn.net/Articles/250967/ > After studying all this material, I do find myself feeling slightly > concerned. The article shows how in C / C++ / assembly you can arrange your > data and order your computations to make maximum use of the various caches > and avoid certain bottlenecks in the system. And the *vast* performance > difference it can yield. But what happens if you happen to be writing your > program in Smalltalk or Java or... Haskell. Up here, you're so far from the > hardware that it would seem that you have *no hope* of using the CPU caches > effectively. Think about it - data scattered all over the heap in an > essentially random pattern, getting moved around periodically by the GC. > [Oh, the GC! That sounds like it must nail the hell out of the cache. And > even if it doesn't, it more or less negates its usefulness because all the > "hot" data is now at a different address.] Just think about trying to > process a Haskell list - all those multiple levels of pointer indirection! > The CPU has no hope of prefetching that stuff... Damn, it seems as if > there's simply no way of ever making Haskell fast. :-(
You're assuming the hardware is constant. "Modern" CPUs were designed back when everyone was using C++; this is changing now, and I for one am still optimistic that CPU designs will follow suit. Stefan
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