Hi everybody, I have tried the latest 2.6.21 kernel + Ingo Molnar's realtime preempt patch (see: http://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO)
And I am really amazed about the results. On my Pentium 4D (dual core) system, 3.2 GHz, I ran the cyclictest application (which is something similar to the "latency" application of Xenomai/RTAI) and I get values below 15 microseconds on my PC (for a single task running with 200 microseconds). Using kernel 2.6.20.4 + Xenomai 2.3.1 I get similar results for the latency application. That means, that Ingo Molnar has done a real cool job in moving standard linux in the direction of a real time OS. However, one thing is not as fine as with Xenomai/rtnet: I want to do real time UDP communication from a user space application. Unfortunately, I was not able to do that as fast as with the Xenomai/rtnet way. My application does a kind of "ping-pong" with an embedded device that is connected as only device to eth1 (Intel e1000 adapter). Using Xenomai/rtnet I get request/response times at about 200 microseconds. When I run an adapted application on the kernel with the preempt patch using the standard linux UDP socket functions (sendto, recv), I get request/response times around 1 millisecond. I have now the assumption that the TCP/IP stack that uses some internal tasks is not running with real time priority. However, I have no idea how to move that code to real time priority or if it makes sense to move it as it is probably not possible to handle only communication via a certain ethernet adapter with real time priority and all other stuff (house keeping via TCP, different Ethernet adapter) with standard priority. Has anybody an idea about the internal behaviour of this or how to continue here? Another approach could be to use a modified version of rtnet on base of the preempt patched kernel. This could allow to use the preempt patch kernel as base for all threads, and the rtnet is used for real time Ethernet communication... Is something like this possible or this there a major error in the approach? Currently, my application is working quite nice using Xenomai/rtnet however there are some drawbacks like the issue with limited IRQs: Sharing of IRQs between Ethernet-Drivers of rtnet and non-realtime drivers is not possible (at least I did not manage that...). A smooth usage of real time features from a "standard" kernel could help here! Thanks for all feedback on this comment! Regards Mathias -- Mathias Koehrer [EMAIL PROTECTED] 50 AMAZON-Einkaufsgutschein bei Bestellung von Arcor-DSL: Viel oder wenig? Schnell oder langsam? Unbegrenzt surfen + telefonieren ohne Zeit- und Volumenbegrenzung? DAS TOP ANGEBOT JETZT bei Arcor: günstig und schnell mit DSL - das All-Inclusive-Paket für clevere Doppel-Sparer, nur 39,85 inkl. DSL- und ISDN-Grundgebühr! http://www.arcor.de/rd/emf-dsl-2 ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ RTnet-users mailing list RTnet-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/rtnet-users
