From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <4A294CAB.3E52.00F8.0@domain.hid> Date: Fri, 05 Jun 2009 16:49:44 +0200 From: "Karl Tyss" References: <4A28F029020000F80002DB14@domain.hid> <4A28FAD4020000F80002DB27@domain.hid> <4A28FAD7.3E52.00F8.0@domain.hid><4A28FAD7.3E52.00F8.0@domain.hid> <4A28E5E0.9020805@domain.hid> <4A2907EF.3E52.00F8.0@domain.hid><4A2907EF.3E52.00F8.0@domain.hid> <4A2920C7.40200@domain.hid> <4A294359.3E52.00F8.0@domain.hid><4A294359.3E52.00F8.0@domain.hid> <4A29290E.7050609@domain.hid> In-Reply-To: <4A29290E.7050609@domain.hid> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Content-Disposition: inline Subject: Re: [Xenomai-help] IRQ-Latency when in idle State on ARM List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org Disabling the I- or D-cache is available as an option by using menuconfig under system-type. As to the Jitters - I didn't describe it correctly what i was doing. I disabled the both caches as a trick to test if there is a difference. The 2 us timing difference was without the caches. With I- and D-cache online i had a difference of 13 us as average value (15us idle and 3 us with user space load) I have to estimate a critical path in order to decide if a timer interrupt driven periodic task or a xenomai periodic task is better for my system. As I noticed this effect of the idle task I had to know why in order to document it or to change the part of the code. Well, now I know what to do and I have to find out if disabling the I-cache is critical at this point and if so, how one can avoid it. My system doesn't have to save power if its online and I suppose that disabling this kind of idleness could be a nice feature in the kernel or xenomai. So thank you for your help again and have a nice weekend, Best regards, Karl Tyss Mit Freundlichen Grüßen, Karl Tyss >>> Gilles Chanteperdrix 06/05/09 4:17 PM >>> Karl Tyss wrote: > Hi, > > 5 minutes ago I found out that one of the caches definately has to > cause the problem. I believe I would have to spent couple of more days > to find out why. > > Your hint was a bulls eye. I tried a dirty trick and commented out the > two lines responsible for disabling the I-cache. It helped. I wonder if > it leads to other problems. I will test it and post my results. > > Thank you both for the quick and productive help. Also, let me insist: 2 microseconds on ARM is peanuts. Really, it is insignificant, you will get much worse jitters than that with a properly loaded system. -- Gilles. --------------------------------------------------------------------------------------- This email including its attachments is intended for the person or entity only to which it is addressed. It may contain confidential and/or privileged material. Any review, forwarding, dissemination, other use of, or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this email in error, please contact the sender and delete the material from any computer system. --------------------------------------------------------------------------------------- Eppendorf AG, Hamburg, Barkhausenweg 1, 22339 Hamburg, Amtsgericht Hamburg HRB 76249 Vors. des Aufsichtsrats: Dipl.-Ing. Adrian Déteindre Vorstand: Klaus Fink (Vorsitzender), Detmar Ammermann, Dr. Heinz G. Koehn, Dr. Michael Schroeder Eppendorf Instrumente GmbH, Hamburg, Amtsgericht Hamburg, HRB 69077 Geschäftsführer: Rainer Treptow Eppendorf Biochip Systems GmbH, Hamburg, Amtsgericht Hamburg, HRB 96641 Geschäftsführer: Dr. Sven Buelow Eppendorf Liquid Handling GmbH, Hamburg, Amtsgericht Hamburg, HRB 92250 Geschäftsführer: Boris von Beichmann