On Fri, Aug 31, 2007 at 09:25:08PM +0530, Girish kathalagiri wrote: > We also had similar problems when where we face these kind of periodic > jitter. In our case we used Intel 82551ER Fast Ethernet Controller( > e100 driver ). The problem with ours was the with the microcode (in > e100.c) of the adapter which had default algorithm where the hardware > was holding of the interrupts until X packets or Y usecs have expired. > > This generated a periodic jitter that was 400-500 us more than the usual one. > This was solved by making the hardware generate interrupt on every frame. > In e100.c this can be done by changing the values of INTDELAY, > BUNDDLEMAX and BUNDDLESMALL (CPU saver parameters) Unfortunately not but it did get me on the right track. The problem is caused by the e100_watchdog function. As far as I can tell e100_watchdog is called from a timer queue and therefore runs with the priority of that thread. And while I set higher priorities for softirq-net-rx and the application I missed the thread for the hardware interrupt of the network interface. So whenever a packet arived while e100_watchdog was running it got delayed. The periodic pattern is a result of this and speed difference of sender and receiver clocks. The jitter is now <50us but still with some periodic patterns. So I'll need to investigate further. michael -- Pengutronix - Linux Solutions for Science and Industry Entwicklungszentrum Nord http://www.pengutronix.de - 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
