On 2011-05-30 09:43, Jonas Witt wrote: > Am 30.05.2011 09:07, schrieb Jan Kiszka: >> On 2011-05-30 09:03, Pavel Machek wrote: >>> On Sat 2011-05-28 16:32:45, Jan Kiszka wrote: >>>> On 2011-05-27 21:11, Gilles Chanteperdrix wrote: >>>>> On 05/27/2011 08:29 PM, Jonas Witt wrote: >>>>>> Sorry, I missed the NTP-part. I am not using NTP. Just plain timer >>>>>> queries on a single system. >>>>>> >>>>>> My clock source is tsc which is the same for Xenomai I suppose. >>>>>> >>>>>> I wonder how a Xenomai task, even if it occupies 50% or even 90% >>>>>> of a 4 >>>>>> milliseconds time slice can interfere with the tsc. The tsc is not >>>>>> incremented via an interrupt, is it? But I do not know much about the >>>>>> inner workings of these functions. >>>>> The problem is not the clocksource, the problem is the timer >>>>> interrupt. >>>>> The kernel expects 1 timer tick every millisecond. >>>> Not on archs that are CONFIG_NO_HZ capable. >>> Umm. NO_HZ is only active while system is idle. Kernel will still >>> expect the periodic ticks when CPU is busy.... >>> >>> (I'm not sure how the compensation works; perhaps it can compensate >>> even while busy..) >> See update_wall_time, the !CONFIG_ARCH_USES_GETTIMEOFFSET includes no >> fixed tick length. >> >> Again, this is also important for Linux when running over hypervisors >> which tend to miss ticks on overcommitment as well. >> >> Jan > > Thanks for the active discussion of the issue. I attached my config. > CONFIG_NO_HZ is activated and I think I disabled all power management > and frequency scaling correctly. Do you think it is worth trying a > kernel with fixed Hz as Gilles suggested? Actually the 1ms Xenomai load > seems to play at least some role in the issue.
For sure, I may also be proven wrong by plain reality. In addition, enable CONFIG_PM and ACPI with the exception of ACPI_PROCESSOR. Who knows what your BIOS is doing in the absence of OS support for this. Jan
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