How do I disable CPU throttling

[Thomas D. Dean]

On 7/12/21 8:17 PM, Paul Procacci wrote:
> 

 > sysctl dev.cpu.0 | grep freq
dev.cpu.0.freq_levels: 3700/4070 2800/2800 2200/1980
dev.cpu.0.freq: 2200

These numbers are in GHz.

What I want to do is understand where the numbers 3700 and 4070 come from.

It seems powerd_profile picks 3700 as the highest value and 2200 as the 
lowest value.

The CPU specs say 4500.

How does the code get the numbers in dev.cpu.0.freq_levels?

I read the code in /usr/src/sys/kern/kern_cpu.c and found a hint
/*
  * Used by the cpufreq core, this function will populate *level with the
  * current frequency as either determined by a cached value
  * sc->curr_level, or in the case the lower level driver has set the
** CPUFREQ_FLAG_UNCACHED flag, it will obtain the frequency from the
** driver itself.
  */
    levels = malloc(count * sizeof(*levels), M_TEMP, M_NOWAIT);
    CPUFREQ_LEVELS(sc->dev, levels, &count)
   /*
    * If still booting and secondary CPUs not started yet, don't allow
    * changing the frequency until they're online.  This is because we
    * can't switch to them using sched_bind() and thus we'd only be
  *** switching the main CPU.  XXXTODO: Need to think more about how to
  *** handle having different CPUs at different frequencies.
    */

The numbers 3700, 4070, 2800, 2200, 1980 can not be changed with boot or 
runtime config.  These values are derived or read from BIOS.

> 
> On Mon, Jul 12, 2021 at 5:01 PM Thomas D. Dean <tomdean at wavecable.com 
> <mailto:tomdean at wavecable.com>> wrote:
> 
>     On 7/12/21 1:12 PM, Paul Procacci wrote:
>      > sysctl's get set generally in /etc/sysctl.conf
>      >
>      > dev.cpu.0.freq_levels <-- This format is called a mib in the native
>      > parlance.
>      > sysctl.conf(5) and sysctl(8) go into much further detail.
>      >
>      > ~Paul
> 
> 
>       > grep -Rail freq_levels /etc/*
>     shows the source of freq_levels
> 
>     I believe this is hardwired somewhere.  Maybe read from the cpu? BIOS?
> 
> 
> Most mib's have defaults.  They are compiled into the kernel statically 
> or made available to it via kernel modules.
> What you are looking for is located in this source file:  
> /usr/src/sys/kern/kern_cpu.c
> 
> Really though, I can tell that's way too much for ya.  Instead what you 
> are looking to do is
> detailed in rc.conf(5):
> 
> "     powerd_enable
>                   (bool) If set to "YES", enable the system power control
>                   facility with the powerd(8) daemon."
> 
> AND
> 
> "     performance_cpu_freq
>                   (str) CPU clock frequency to use while on AC power.  The
>                   string "LOW" indicates that cpufreq(4) should use the 
> lowest
>                   frequency available while "HIGH" indicates that the 
> highest
>                   frequency (less power savings) should be used."
> 
> What you want to most likely do is the following:
> 
> echo powerd_enable=\"YES\" >> /etc/rc.conf
> echo performance_cpu_freq=\"HGH\" >> /etc/rc.conf
> 
> Follow that up by restarting the powerd daemon:
> 
> /etc/rc.d/powerd restart
> 
> If you have a supported cpu, which I have no reason to believe 
> otherwise, your
> goal of running your machine at full speed without throttling should be 
> within your grasp.
> 
> powerd, a userland daemon, controls this mib as necessary on the fly.
> 
> rc.conf(5) is a godsend for stuff like this and its documentation is 
> amazing.
> 
> On another note, I see no reason to change this at all.  CPU's are 
> nearly instantaneous
> at scaling as necessary to accomodate loads for their needs.  I digress 
> however.
> 
> Take Care.