I just stumbled upon an idea (yet untested) to improve latency with RT_PREEMPT on multicore cpu's like the atom
this assumes that rtapi_app in sim mode (plus hal_parport in usermode) will be the time-critical component it borrows from the isolcpus=1 idea for RTAI where CPU1 would be reserved for the base thread the idea is to do something similar for rtapi_app: quote from: Max Krasnyansky's post in http://www.digipedia.pl/usenet/thread/19080/11385/ > Actually this is kind of available right now with vanilla 2.6 kernel. > I'm talking about CPU reservation. Here is an example. > Let's say we have dual CPU box and we want to dedicate CPU 1 to > our application: > - Configure the kernel with following boot options: > isolcpus=1 acpi_irq_nobalance noirqbalance > > This excludes CPU 1 from the scheduler balancing logic. And disables > ACPI and SW irq balancing. > Make sure that you don't run user-space IRQ balancer. > > - Redirect all interrupts to CPU 0 > for i in /proc/irq/*; do > echo 1 > $i/smp_affinity; > done > > - Your app call now migrate to CPU 1 > int cpu = 1; > uint32_t mask = (1 << cpu); > sched_setaffinity(0, sizeof(mask), (cpu_set_t *) &mask); > > That's it. CPU 1 is yours. There will be almost zero activity on it, besides > your task of course. > > Max what would needed to be done is to add the sched_setaffinity() code fragment to rtapi_app and do the boot/setup incantations before starting linuxcnc - Michael Am 14.09.2012 um 15:46 schrieb Kent A. Reed: > Thanks, Jan, Lars, Michael, Charles, Ken, and Steve for your thoughts. > > I'll have to cogitate a bit on what to do next, but I can answer Steve > off the top of my head. Two pre-built realtime kernels are available > from the Debian Wheezy repository. The amd64 build is for 64-bit amd and > intel processors; there is also a 32-bit 3.2.0-3-rt-686-pae build. > That's what I alluded to in my third agenda item to try. > > <muttered aside> > Yes, I know I could custom-build my own kernel, but there comes a point > where I say "enough, this isn't just tweaking any more." It took > LinuxCNC (well, ok, EMC2) a while to get to the point where a LiveCD > distribution just works for most folk. I'm hoping it doesn't take as > long for our use of these alternative realtime platforms to stabilize in > the same way, especially since I believe they are necessary > alternatives. If using RT PREEMPT or Xenomi approaches requires more > than a straightforward tuning-your-system checklist, then I don't know > how we'll make the alternatives attractive to our user base let alone > attract new classes of users. That would be unfortunate. > </muttered aside> > > It's clear to me from your responses that if I want to run with the big > dogs I have to learn how to instrument a realtime environment :-) > > Regards, > Kent > > > On 9/14/2012 8:05 AM, Steve Stallings wrote: >> Hi Kent, >> >> I have NO experience with doing this sort of build, >> but have to wonder if it is significant that your >> target is an Atom D510 cpu, yet you list a kernel >> for amd64. >> >> Regards, >> Steve Stallings >> >>> -----Original Message----- >>> From: Kent A. Reed [mailto:kentallanr...@gmail.com] >>> Sent: Thursday, September 13, 2012 11:31 PM >>> To: EMC developers >>> Subject: [Emc-developers] question re RT PREEMPT linux on >>> ASUS Atom board >>> >>> >>> <blah blah blah> > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ Everyone hates slow websites. So do we. Make your web apps faster with AppDynamics Download AppDynamics Lite for free today: http://ad.doubleclick.net/clk;258768047;13503038;j? http://info.appdynamics.com/FreeJavaPerformanceDownload.html _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
