Messages in this thread | | | Subject | Re: 2.6.14-rt21: slow-running clock | From | john stultz <> | Date | Tue, 06 Dec 2005 20:01:10 -0800 |
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On Wed, 2005-12-07 at 14:09 +1030, Jonathan Woithe wrote: > > > When running Ingo's 2.6.14-rt21 (and in fact rt kernels back to at least > > > 2.6.13-rc days), the clock on my i915-based laptop runs slow. The degree > > > of slowness appears directly related to how busy the machine is. If > > > it is just sitting around doing very little the time is kept rather > > > well. However, as soon as the load increases the RTC and system time > > > diverge significantly. For example, running jackd for 2 minutes results > > > in the system time loosing as much as 20 seconds compared to the CMOS RTC. > > > Processes doing HDD I/O also seem to affect the system time similarly. > > > > > > Selectively disabling different timer-related kernel options does not make > > > any difference. However, the clock seems fine under vanilla 2.6.14, > > > suggesting an issue somewhere in the rt patches. > > > > Could you please send me your dmesg and the output of: > > > > cat /sys/devices/system/clocksource/clocksource0/* > > First the contents of the above /sys/ files: > > /sys/devices/system/clocksource/clocksource0/current_clocksource: > c3tsc > > /sys/devices/system/clocksource/clocksource0/available_clocksource > acpi_pm jiffies c3tsc pit
Odd. I'm not sure why the acpi_pm wasn't chosen by default if it was available and the TSC fell back to the c3tsc. It might be something in the -RT tree that's changed that bit. Could you try the following and see if it doesn't resolve the timekeeping problems you're seeing?
echo "acpi_pm" > /sys/devices/system/clocksource/clocksource0/current_clocksource
Still it sounds like something isn't right w/ either the c3tsc code or the cpufreq notification code. Would you be willing to test further patches?
Also could you try booting w/ idle=poll and see if that changes the behavior?
Thanks for the testing and feedback! -john
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