Re: x86_64 dynticks not working prev: cpuidle, dynticks compatible or no?

Ed Sweetman
2007-12-08T04:56:17Z

Robert Hancock wrote:
> Ed Sweetman wrote:
>> System is idle now, previously it was doing something i couldn't halt
>> at the time. I'm looking at "Local timer interrupts" in the "Loc:"
>> section of /proc/interrupts.
>> Across 1 second while the system is pretty much idle, i still get 300
>> interrupts. My HZ variable is set to 300 in the kernel config, so
>> this is expected but I was under the assumption that
>> dynticks/tickless being compiled in would cause that to be much lower.
>>
>> Am I reading the wrong section of /proc/interrupts to verify if
>> dynticks is working or not? Again, i see no difference in cpu temp at
>> all.
>
> Try running powertop ( http://www.lesswatts.org/projects/powertop/ )
> and see what it reports.
>
> I don't think dynticks will generally save huge amounts of power on a
> typical desktop machine. The big gains come from being able to stay in
> deep sleep C-states (C2/C3) for longer periods of time, but most
> desktop machines only enable sleep states down to C1.
>
I tried running powertop, it complains about not having timer
statistics, I looked throughout the kernel config for a timer stat
option, but can't find one.

I didn't have hpet compiled in, i'm not sure if this is required but a
lot of places seem to suggest hpet and high precision timer and tickless
be compiled together. I also disabled cpuidle and i'll reboot and try
that.

>>
>> In case it helps, this is an athlon64 x2 with apic functioning and
>> both cores active in 64bit mode. dmesg is below.
>> not related :
>> Some additional notes: it87 is my lm_sensor, it doesn't work in this
>> kernel, yet it did in 2.6.22. Perhaps enabling high precision timers
>> changed something in acpi land.
>>
>> I enabled tcp dma offloading in this kernel, i get debugging output
>> related to it, error is at the last line. No corruption or otherwise
>> bad behavior. Transferring via cifs at 9.7MB/sec "incoming" took
>> about 15% of one cpu... I never bothered to check if that is the
>> norm but i suspect i'll be removing that feature as it seems to not
>> play nice with the kernel.
>