ACPI-fast default timecounter, but HPET 83% faster

John Baldwin jhb at freebsd.org
Thu Apr 30 21:41:24 UTC 2009


On Sunday 26 April 2009 10:27:42 pm Garrett Cooper wrote:
> I'm seeing similar results.
> 
> [root at orangebox /usr/home/gcooper]# dmesg | grep 'Timecounter "'
> Timecounter "i8254" frequency 1193182 Hz quality 0
> Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
> Timecounter "HPET" frequency 14318180 Hz quality 900
> [root at orangebox /usr/home/gcooper]# ./cgt
> 1369355
> [root at orangebox /usr/home/gcooper]# sysctl
> kern.timecounter.hardware="ACPI-fast"
> kern.timecounter.hardware: HPET -> ACPI-fast
> [root at orangebox /usr/home/gcooper]# ./cgt
> 772289
> 
> Why's the default ACPI-fast? For power-saving functionality or because
> of the `quality' factor? What is the criteria that determines the
> `quality' of a clock as what's being reported above (I know what
> determines the quality of a clock visually from a oscilloscope =])?

I suspect that the quality of the HPET driver is lower simply because no one
had measured it previously and HPET is newer and less "proven".

-- 
John Baldwin


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