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

Ed Sweetman
2007-12-08T05:28:50Z

Ed Sweetman wrote:
> 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.
>
read too fast through the powertop error message. timer stat info is in
kernel_debug option. Which i did not compile in this latest kernel
again. Sorry.

Though, with hpet and such, i still see no measurable difference or any
sort of evidence that ticks are being skipped (comparing
/proc/interrupts across sleep 1s;)

>
>>>
>>> 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.
>>
>