On Thu, Mar 04, 2010 at 01:29:53PM +0100, M. Koehrer wrote: | Hi all! | | I am running the RT_PREEMPT kernel 2.6.31.2-rt13 on a Intel Quad Core CPU. | I start my kernel with isolcpus=1-7 option to force all processes to run on CPU core 0 only. | Now we have the need for a very fast loop. Within this loop some accesses from/to a PCIe I/O board | (mapped in user space) and some additional computation has to be done. | For this, I use a real time thread, run this on CPU core 3 and let it run in an endless polling loop. | So far everything works fine. | This thread is the only running user mode thread on CPU core 3. | However, we measure some run time jitters when accessing the I/O board in the range of up to | 15 microseconds which are not tolerable by the application. | I see that on all cores the "Local Timer Interrupt" occurs 100 times a | second (of course this is the timer frequency select in the kernel configuration). Are CPU0 and CPU3 on the same socket? Are you using a SMP or a NUMA box? I would suggest running your application in a CPU on a different socket just to ensure you are not having any cache issues. Have you tried running hwlat_detect or smi-test? Your 15us threshold is pretty tight and could easilly be affected by SMI spikes (if present in your system). Luis | My question is now: | Is it possible to disable the "Local Timer Interrupt" for core 3 as it is actually not required here? | I want to use the full 100% CPU core time for this single loop. | | Any help or ideas are welcome! | | Thanks a lot. | | Regards | | Mathias | | -- | Mathias Koehrer | mathias_koehrer@xxxxxxxx | | | Tolle Dekolletés oder scharfe Tatoos? Vote jetzt ... oder mach selbst mit und zeige Deine Schokoladenseite | bei Topp oder Hopp von Arcor: http://www.arcor.de/rd/footer.toh | -- | To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in | the body of a message to majordomo@xxxxxxxxxxxxxxx | More majordomo info at http://vger.kernel.org/majordomo-info.html ---end quoted text--- -- [ Luis Claudio R. Goncalves Bass - Gospel - RT ] [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ] -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
