Gentle persons: First, a statement.
On my ASUS AT5NM10-I board (Intel Atom D510 CPU, 2GB RAM, yada yada yada) I followed in Charles Steinkeuhler's footsteps (http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Debian_Wheezy_Linux-Rt_Compile_LinuxCNC) to build a 64-bit Debian Wheezy RT PREEMPT Linux system running the 3.2.0-3-rt-amd64 kernel and Linuxcnc 2.6.0~pre. Such a build has given Charles some decent albeit not (yet) great latency numbers on several non-Atom boards. My ASUS board has given me excellent latency results with what I'll call classic Ubuntu 10.04LTS LinuxCNC running the 2.6.32-122-rtai kernel: sub 10us for both threads with Hyperthreading disabled in the BIOS and one cpu isolated during the boot process. With the RT PREEMPT system, this board gives lousy results even running headless. Using latency-test, for some minutes I see the base (25us) thread showing a max latency of anywhere from 25us to 40us and the servo (1000us) thread 40us to 50us. Then, the servo thread pops a bit and the base thread pops a lot, to about 110us. At the same time, the kernel throws three lines to the console "ERROR: Missed scheduling deadline for task 0 [nnnn times] "Now is xxxxx.xxx, deadline is xxxxx.xxx "Absolute number of pagefaults in realtime context: 1030" This process repeats but not at regular intervals. Using latencyplot, I can see that, with nothing else running, both threads mostly show good latency numbers, typically < 10us, once we've settled down after invoking latencyplot. If I run a copy of glxgears, the servo thread latency gets jumpy but stays below about 40us. Running several copies of glxgears doesn't seem to cause any more damage, nor does invoking du or some other disk access-intensive command. Sooner or later, though, the above big-time event happens. Repeat ad nauseum. I've done everything I can think of. I've diddled all available BIOS settings (this is not an enthusiast board; it has only a limited number of settings); stopped the kernel from loading just about any non-essential module; preventing many services from starting. No gdm, no X, no Intel i915 driver, no acpid, no alsa, no pulseaudio, yada yada yada. About the only things I haven't tried are (1) trying Charles' suggestion of playing with cpusets, mostly because I don't understand them well enough yet to trust myself, (2) ripping out some more modules that relate to sound (with names snd*; alsa and pulseaudio stuff is already gone), mostly because I'm not sure who's loading them, and (3) redoing all this with a 32-bit Debian Wheezy, mostly because getting Debian Wheezy systems into this machine is a bore (the Wheezy installer is broken somewhere in the disk partitioning process and why should I be the one to fix it when others have been complaining forever). Now, my question. I'm wondering if my results are intrinsic to the Atom architecture or specific to the ASUS BIOS. Has anyone with a different Atom board, preferably an Intel-branded board, loaded and tested Wheezy with Linux-RT and LinuxCNC? If so, what's your experience? Regards, Kent ------------------------------------------------------------------------------ Got visibility? Most devs has no idea what their production app looks like. Find out how fast your code is with AppDynamics Lite. http://ad.doubleclick.net/clk;262219671;13503038;y? http://info.appdynamics.com/FreeJavaPerformanceDownload.html _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
