Laptop battery life on FreeBSD

Shawn Badger shawnbadger at
Tue Jan 27 20:41:19 PST 2009

Chuck Swiger wrote:
> On Jan 27, 2009, at 4:49 PM, Shawn Badger wrote:
>>> Have you tried reducing HZ to 100 (put kern.hz="100" in 
>>> /boot/loader.conf and reboot)?
>>> Are you running powerd?  Look into "sysctl hw.acpi" and "sysctl 
>>> debug.cpufreq"....
>> Thanks for the ideas Chuck.  I lowered kern.hz to 100 as you 
>> suggested (does this affect the kernel's ability to track time in 
>> milliseconds?  ie. if I want to run a benchmark using the 'time' 
>> utility?).
> Changing the scheduler quantum won't affect the system clock or the 
> ability to do millisecond-level timing of userland processes.  It does 
> affect the granularity of things like ipfw/dummynet if polling is 
> enabled, but shouldn't have any real negative effects otherwise.
> For most of Unix history, HZ=100 was a common default, and the reduced 
> context switch frequency should result in a decent improvement to 
> power drain.  If you have a concern, consider comparing against HZ=250 
> and see how the battery life and responsiveness or granularity of 
> network traffic, etc feel....

Thanks for the info.  I'll definitely do some tests and find a good 

>> And the output of the two sysctl queries is posted here:   
>> I'm not very familiar with acpi, so if you see anything that could be 
>> optimized, I'd appreciate the feedback.
> I have limited experience with running FreeBSD on a laptop personally 
> [1], so others will likely have more relevant feedback; I'm just aware 
> of some starting points.  :-)
> Regards, -- 
> -Chuck
> [1]: I've helped a few people run FreeBSD 5.x/6.x on various IBM 
> ThinkPads (circa T.42s) an maybe an HP Pavillion or Dell Latitude, and 
> I've run FreeBSD a bit on a Mac mini and a MacBookPro (2,2), but I 
> don't use FreeBSD on a laptop regularly...I think of it as a server 
> OS.  :-)

I too generally think of FreeBSD as a server OS, but I just can't get 
over how nice the development environment is - hence the laptop. 


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