In article <mailman.2810.1321562763.27778.python-l...@python.org>, Tycho Andersen <ty...@tycho.ws> wrote:
> While I agree there's a lot of things you can't control for, you can > get a more accurate picture by using CPU time instead of wall time > (e.g. the clock() system call). If what you care about is mostly CPU > time [...] That's a big if. In some cases, CPU time is important, but more often, wall-clock time is more critical. Let's say I've got two versions of a program. Here's some results for my test run: Version CPU Time Wall-Clock Time 1 2 hours 2.5 hours 2 1.5 hours 5.0 hours Between versions, I reduced the CPU time to complete the given task, but increased the wall clock time. Perhaps I doubled the size of some hash table. Now I get a lot fewer hash collisions (so I spend less CPU time re-hashing), but my memory usage went up so I'm paging a lot and my locality of reference went down so my main memory cache hit rate is worse. Which is better? I think most people would say version 1 is better. CPU time is only important in a situation where the system is CPU bound. In many real-life cases, that's not at all true. Things can be memory bound. Or I/O bound (which, when you consider paging, is often the same thing as memory bound). Or lock-contention bound. Before you starting measuring things, it's usually a good idea to know what you want to measure, and why :-) -- http://mail.python.org/mailman/listinfo/python-list
