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

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Date:	Fri, 07 Dec 2007 23:56:00 -0500
From:	Ed Sweetman <safemode2@...cast.net>
To:	Robert Hancock <hancockr@...w.ca>
CC:	linux-kernel@...r.kernel.org
Subject: Re: x86_64 dynticks not working   prev: cpuidle, dynticks compatible
 or no?

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.
>

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