paul_c wrote: > > Running a minimal script that just burns CPU cycles is of little value - An > analogy would be to jack up the wheels of a car and run the engine to the red > line and claim it will do 150MPH.
Of course not, and that isn't what I was saying. Both SWP and I have observed that with an SMP RTAI kernel, running a simple do-nothing loop IN ADDITION to all the other things that we normally do during a latency test results in better overall maximum latency numbers. I don't know the mechanism, and was only speculating in my previous message. It could also be that the busy-loop keeps the Linux idle process from running (on at least one core), and the idle process does something that hurts latency. Maybe it slows the clock, or puts the CPU into a halt or sleep state so that it needs a bit of extra time to resume. My observations were on a Core2 Duo, with an Intel 975XBX2 motherboard. I haven't consistently seen the same effect with the Atom CPU/mobo combo. From what I can tell, the Atom doesn't slow the clock during idle periods, while the Core 2 does - maybe that is why the busy-loop makes a difference on one board and not the other... > What you _should_ be doing is providing some real-world loads over an > extended > period, i.e: > > Start the RTAI latency test then: > > dd if=/dev/urandom of=/dev/null > ping -f -s 1600 -l 1000 localhost # also flood-ping from another box. > cd <kernel-src>/ && make -j > For more extreme testing, run cpuburn or (forkbomb). Starting up X > while the latency-test is running will also give the system a good > short term loading, and if it doesn't lock up starting/stopping X, > then you will have a solid setup. With X running, any graphics > intensive processes will also provide a good workout - Try some of > the OpenGL screensavers. I typically run glxgears, do a cvs update to get some network activity, and do a make clean ; make on my EMC2 source tree. Not quite as severe as what you listed above, but the same general idea. Regards, John Kasunich ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
