On Mon, Apr 2, 2012 at 4:28 PM, Mike S <[email protected]> wrote: > I've got a Trimble Thunderbolt PPS source for NTP, Linux 2.6.35, on a quad > core CPU. PPS source is coming into a multiport serial card, which > /proc/interrupts shows is sharing IRQ with some inactive USB ports (IRQ 17). > > Running normally, I'll get about +- 20 us ptp of jitter (as reported by ntpq > -p, and in loopstats). If I load up the CPU, jitter will shrink to +- 1-3 > us. I've played around with different cpufreq setting, thinking it might be > related to the processor speed during an IRQ, but that seems to have minimal > impact (performance vs. conservative vs. ondemand). >
I think your CPU goes into some power saving mode when there is no load and takes some number of micro seconds to wake up after an interrupt. Keeping a load on it prevents the sleep or power save mode and hence the need to "wake up." -- Chris Albertson Redondo Beach, California _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
