Phenom II X6 1100T - Prevent frequency from fluctuating in Linux?

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iissmart

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Jan 27, 2011
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I have a Phenom II X6 1100T in a Gigabyte GA-MA790XT-UD4P and I am desperately trying to lock down the CPU frequency for timing purposes. This is an Ubuntu 16.04 server. I'm not trying to overclock it, I just want all cores to stay at 3300 MHz forever, regardless of load.

Summary of changes so far:
* Disabled AMD Turbo Core in BIOS
* Disabled all Advanced Clock Calibration settings in BIOS
* Disabled AMD C1E support in BIOS
* Disabled HPET in BIOS
* Specified CPU multiplier to result in 3300 MHz frequency in BIOS (instead of Auto)
* Specified CPU Host Clock Control to 200 MHz in BIOS (instead of Auto - to disable CPU Spread Spectrum)
* Specified CPU Northbridge frequency to 2000 MHz (instead of Auto)
* Specified PCI-E clock to 100 MHz (instead of Auto)
* Specified HT Link Frequency to 2000 MHz (instead of Auto)
* Specified kernel parameter "intel_idle.max_cstate=1" or "intel_idle.max_cstate=0" (seemed to have no effect)
* Installed turbostat, cpufrequtils, cpupower utilities

As of right now the CPU cores fluctuate very slightly from 3312.0 +/- 3.0 MHz at 0% load. At 100% load they peg to 3315.050 MHz +/- 0.001 MHz, which is better, but still causes timing issues. On other systems available to me (with different motherboards/CPUs) I observe a constant CPU frequency regardless of load.

I feel like the utilities I've tried (turbostat, cpufrequtils, cpupower) are not working as they should. Turbostat reports an average MHz of around 40 Mhz at 0% load and doesn't report c-states with the --debug flag as documented on the internet. cpufreq-info just shows "no or unknown cpufreq driver is active on this CPU" and attempting to change governor settings says "Error setting new values". cpupower frequency-info says "Unable to call hardware".

At this point I am at a loss as for what to try next. I don't see any mention of a governor in dmesg or in /sys so I'm not sure whether I can change that (maybe it's not there with the BIOS settings I have disabled?).

Any thoughts or experience that might help me out?
 
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seems like fsb fluctuation maybe. try manually setting it instead of auto.
 
I've never had a board that locked down to exactly the rated speeds. There is always going to be some fluctuation in the bus speed. As I'm sitting here right now my Ryzen 2700X on CH7 board is fluctuating between 99.35 and 99.77 and that's a decently high end CPU/board.
 
kirbyrj said:
I've never had a board that locked down to exactly the rated speeds. There is always going to be some fluctuation in the bus speed. As I'm sitting here right now my Ryzen 2700X on CH7 board is fluctuating between 99.35 and 99.77 and that's a decently high end CPU/board.
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I have AMD Athlon systems running RHEL at work that report a constant "xxx.000 MHz" frequency, so I'm sure it's possible. They are even older than this however.

pendragon1 said:
seems like fsb fluctuation maybe. try manually setting it instead of auto.
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CPU Host Clock Control should lock that down but setting it to Manual 200 MHz didn't seem to help.
 
due to cpu changes over the years probably has to do with how the clocks are reported.. back in the day it was just static clocks based on the cstate even though the clock rate fluctuated anyways without it reporting the change. now that cpu's use a variable clock speed i'm guessing the programs are now reading that fluctuation. at idle it should fluctuate a lot more than load.
 
iissmart said:
I have AMD Athlon systems running RHEL at work that report a constant "xxx.000 MHz" frequency, so I'm sure it's possible. They are even older than this however.


CPU Host Clock Control should lock that down but setting it to Manual 200 MHz didn't seem to help.
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it the fsb is still on auto its not locked.
 
well if you have the fsb and multi set to manual and power profile is set to 100% cpu, then its just how it is. some boards bounce like that, a 1600 system I built does it.
 
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