From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Luis Claudio R. Goncalves" Subject: Re: Disabling lapic timer for a certain core Date: Thu, 4 Mar 2010 11:04:53 -0300 Message-ID: <20100304140453.GX2553@uudg.org> References: <14900780.1267705793289.JavaMail.ngmail@webmail16.arcor-online.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-rt-users@vger.kernel.org To: "M. Koehrer" Return-path: Received: from mail-vw0-f46.google.com ([209.85.212.46]:40945 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753153Ab0CDOFE (ORCPT ); Thu, 4 Mar 2010 09:05:04 -0500 Received: by vws9 with SMTP id 9so1236696vws.19 for ; Thu, 04 Mar 2010 06:05:02 -0800 (PST) Content-Disposition: inline In-Reply-To: <14900780.1267705793289.JavaMail.ngmail@webmail16.arcor-online.net> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Thu, Mar 04, 2010 at 01:29:53PM +0100, M. Koehrer wrote: | Hi all! |=20 | I am running the RT_PREEMPT kernel 2.6.31.2-rt13 on a Intel Quad Core= CPU. | I start my kernel with isolcpus=3D1-7 option to force all processes t= o run on CPU core 0 only. | Now we have the need for a very fast loop. Within this loop some acce= sses from/to a PCIe I/O board | (mapped in user space) and some additional computation has to be done= =2E | 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 boar= d in the range of up to=20 | 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 co= nfiguration). 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 j= ust 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 i= t is actually not required here? | I want to use the full 100% CPU core time for this single loop. |=20 | Any help or ideas are welcome! |=20 | Thanks a lot. |=20 | Regards |=20 | Mathias |=20 | --=20 | Mathias Koehrer | mathias_koehrer@arcor.de |=20 |=20 | Tolle Dekollet=E9s oder scharfe Tatoos? Vote jetzt ... oder mach selb= st 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-us= ers" in | the body of a message to majordomo@vger.kernel.org | More majordomo info at http://vger.kernel.org/majordomo-info.html ---end quoted text--- --=20 [ 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-user= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html