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

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Date:	Sat, 08 Dec 2007 00:28:39 -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?

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.
>>
>

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