Author: Tom Kerrigan
Date: 18:53:17 10/04/03
Go up one level in this thread
On October 04, 2003 at 21:49:48, Gian-Carlo Pascutto wrote: >On October 04, 2003 at 21:40:59, Tom Kerrigan wrote: > >>(Quick aside: very shortly after HT first came out, a patch for Linux was >>released to "support" HT--the purpose was not to allow you to use the extra >>logical processors (because they're transparent to the OS) but to solve exactly >>the problem you mention. > >2.6.x is the first kernel to have improvements in this regard, >meaning that all normal Linux systems do _not_ have this >optimization yet. > >>I assume Microsoft also made a similar fix and I don't >>know which versions of Windows have it, but I am running a version of Windows >>that would.) > >You don't know, but you do know? Well, let's say I have the latest version of Windows. >>Given that, HT would have to be providing a 50% speedup for my program if it >>were only running on one processor, which seems unrealistically high, and that >>also means my program should run 100% faster with 4 threads (vs. 2) but in >>reality it only runs 15% faster. > >I don't get your math. Put another way, if 2 threads are spending a bunch of time on just 1 processor, that means the 2nd processor has a bunch of idle processing power. So if I run 4 threads, it should use the extra processing power and run a lot faster, but it doesn't. The conclusion is that when running 2 threads, each thread gets its own CPU. -Tom
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