problems getting AMD C-70 APU working with powerd/cpufreq

[tech-lists]

Hi, thanks for taking the time to look at this,

On Sat, Oct 14, 2017 at 10:36:02PM +1100, Ian Smith wrote:
>On Fri, 13 Oct 2017 13:37:21 +0100, tech-lists wrote:
> > Hi,
> >
> > I have a netbook with amd c-70 cpu and am trying to get powerd
> > to work with it. Will this chip not work with cpufreq/powerd?
>
>Perhaps not.

oh well!!
>
> > system: FreeBSD 11.1-STABLE #0 r324342
> >
> > # sysctl debug.cpufreq.verbose=1
> > debug.cpufreq.verbose: 0 -> 1
>
>This shows that cpufreq was alreasy loaded.  It's in the GENERIC kernel.
>Have a good browse through cpufreq(4).

I can't comment about earlier versions of FreeBSD, but this sysctl 
is present on 11.1-stable without cpufreq loaded. I'm using a modified 
kernel - modified to the extent that superfluous stuff has been 
removed, because this machine is hardware-challenged. Without cpufreq 
loaded, the following sysctls are present:

# sysctl -a | grep cpufreq
debug.cpufreq.verbose: 0
debug.cpufreq.lowest: 0

# uname -i
ACER
# cat /sys/amd64/conf/ACER |grep cpufreq
#
# cat /boot/loader.conf 
amdtemp_load="YES"
#

I've known this machine has had issues with cpufreq for a while, but
this is the first time I've sat down to try work out why. This is one
of the reasons why cpufreq isn't in my kernel.

which is why I was able to

> > # kldload cpufreq
> > #

no message

(I set debug.cpufreq.verbose to 1 in order to hopefully see more
output)

> > dev.acpi_perf.1.%parent: cpu1
> > dev.acpi_perf.0.%parent: cpu0
>
>These are interesting.  In cpufreq(4) you'll see acpi_perf is one of the
>absolute frequency control drivers, presumably used (see also in dmesg)
>because the expected driver for AMD processors, powernow, did not attach
>- though your verbose dmesg shows nothing about any failure/s to attach.
>
> > dev.cpu.1.cx_method: C1/hlt C2/io
> > dev.cpu.1.cx_usage_counters: 237351 1893186
> > dev.cpu.1.cx_usage: 11.14% 88.85% last 156us
> > dev.cpu.1.cx_lowest: C2
>
>At least you're getting plentiful use of C2 state, though I'm not aware
>how much power saving that might buy you on that AMD CPU.

Not a lot! ;)

One of the reasons I'm interested in powerd/cpufreq is that I beleive it
can make turbo kick in. Apparently this chip has a turbo mode @1.333GHz.

might be wrong about that though.

>So, there's no dev.cpu.0.freq nor dev.cpu.0.freq_levels - therefore
>powerd has nothing to work with.  Its (misleading?) message doesn't mean
>cpufreq not loaded, but that the sysctls powerd relies upon don't exist.

[...]

>Nothing in any of those suggests that this cpu has any other frequency
>available than 1000MHz, which seems quite bizarre to me.  Of course it's
>possible FreeBSD hasn't been taught to recognise this particular cpu.
>
>You haven't disabled anything in $BIOS related to power or freq control?

The bios has only a very limited number of options for this machine - 
possibly by design as the machine is a netbook. Options for overclocking 
are not present at all.

>The cpuid output has a heading "Advanced Power Management Feature Flags"
>near the bottom, but none are shown.

yeah, odd that

>Hope someone else has something more useful to offer, and thanks for
>mailing me those files when my browser was deemed too old for your site.

thanks again for your help
-- 
J.