Yes, that was my educated guess too. - that the empty loop causes better distribution of tasks, namely that they remain in the same core and computing is not distributed for one task between two cores. But for the hardware part: cache prediction, jump prediction (and cache miss) may also be affected in hardware, so it is not 100% clear if and how a software solution would be possible. Remember that the loop is a series of jumps so that caching has altered behaviour too. Does anybody know what is the performance on four-cored x86 machines?
On Mon, Feb 9, 2009 at 6:29 PM, Jon Elson <el...@pico-systems.com> wrote: > John Kasunich wrote: >> My own theory (and it is only a theory) about why the cpu hog works is >> related to cache. The hog uses very little memory, and since it keeps >> one CPU busy, that CPU never runs any other code. So the RT code >> doesn't get flushed out of cache, and doesn't have to get fetched back >> into cache later. >> >> > I think you have to be right, here. The trick is to make sure the RT > tasks never hop from one CPU to another. Probably having a process > always ready to run on one CPU makes the choice easy for the RT > scheduler to pick the same CPU always for the RT threads. > > The CPU hog doesn't get complete use of a CPU, it has to share the CPU > with all other user-mode processes. What it does is guarantee that that > CPU always has a process ready to run. > > It seems there ought to be a cleaner way to achieve this result, but I > have no idea how easy it is to configure the RT scheduler's rules. What > about the scheme that reserves one core for RT threads only? Does that > alter this result? > > Jon > > ------------------------------------------------------------------------------ > Create and Deploy Rich Internet Apps outside the browser with Adobe(R)AIR(TM) > software. With Adobe AIR, Ajax developers can use existing skills and code to > build responsive, highly engaging applications that combine the power of local > resources and data with the reach of the web. Download the Adobe AIR SDK and > Ajax docs to start building applications today-http://p.sf.net/sfu/adobe-com > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > ------------------------------------------------------------------------------ Create and Deploy Rich Internet Apps outside the browser with Adobe(R)AIR(TM) software. With Adobe AIR, Ajax developers can use existing skills and code to build responsive, highly engaging applications that combine the power of local resources and data with the reach of the web. Download the Adobe AIR SDK and Ajax docs to start building applications today-http://p.sf.net/sfu/adobe-com _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
