cpuinfo current speed greater than max speed

[tashirosgt]

In putting together a system with an Athlon quad core processor ( Family 21, model 1, according to cpuinfo), I find that /proc/cupinfo shows "max speed" is 3200 MHz and "current speed" is "3600 MHz". Is there something non-obvious about the definition of "max speed" ?

[DBelton]

cpuinfo is a piece of crap as far as I am concerned.

It sees my processor that is running over 2.2Ghz as only able to run 1.8Ghz

[    0.000000] Detected 2257.442 MHz processor.

and clip from /proc/cpuinfo:

cpu MHz		: 1800.000

and unless I disable the performance/ondemand governeor I can't run at the full speed of the processor as it will only allow 1.8Ghz as the maximum setting.

Easiest way for me to force the full speed of the processer is to disable speedstep in the BIOS so the OS can't scale it back.

[george_toolan]

Please check the data sheet for your cpu. With turbo core it is probably allowed to run faster than "max" speed which is a bit misleading.

"Max" obviously refers to the fastest speed you or the kernel can select manually and then the cpu decides if it can run even faster than that ;-)

Try powertop to get a more detailed reading of cpu states.

[DBelton]

My CPU doesn't have anything like "turbo core" it's a standard Dual Core Pentium 4, not even the core 2 duo.

My CPU runs at 2257.442 MHz and the kernel detects it properly. cpufreq (which sets the cpuinfo) detects it at 1800 MHz and will not allow anything to set the maximum CPU speed above 1800MHz. So if the CPU is ever scaled (with the ondemand governor, for example) then it will never get set back to it's maximum speed, since 1800 MHz is the maximum speed that is set by cpufreq. I have tried to manually set the max cpu speed, but it won't allow anything to set it above 1800 MHz.

cpufreq (and by result, cpuinfo) are totally useless (actually worse than useless since they cause problems) on my machine.

[george_toolan]

The original post was about some AMD quad core.

I'm not even sure if a Pentium 4 supports frequency scaling.

On a modern system you'll have to enable Intel Speedstep Technology (EIST) in your BIOS.

[tashirosgt]

I was incorrect to attribute the cpu speed info to /proc/cpuinfo. (I was looking at a file and I forgot what produced it). The speed info is output by the command dmidecode.

[DBelton]

the pertinent lines from dmidecode here:

	External Clock: 200 MHz
	Max Speed: 1800 MHz
	Current Speed: 2400 MHz
	Status: Populated, Enabled
	Upgrade: Socket LGA775

Notice that Max Speed is shown as much less than the Current Speed. If I enable any of the CPU scaling governors in cpufreq, then the fastest it will ever set the processor is to 1800MHz, and I have been unable to force the Max Speed to anything greater than 1800 MHz.

[tashirosgt]

That output illustrates my question. What is the meaning of "max speed" and "current speed"? If I interpret those phrases simplistically, current speed should never be more that max speed.

[DBelton]

Max speed is set by cpufreq when the system boots.

In my case, cpufreq sets Max Speed to 1800 MHz, even though the processor is running at 2400 MHz. The kernel detects it properly, but cpufreq doesn't.

Once cpufreq decides that 1800 MHz is the maximum speed, nothing I do can set it faster if it ever is scaled down. So, I have to disable EIST in the BIOS to prevent cpufreq from scaling the speed back if I want to be able to run the CPU at the proper speed instead of the slower 1800 MHz.

[george_toolan]

Interesting program

        Version: Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
        Voltage: 0.0 V
        External Clock: 100 MHz
        Max Speed: 3800 MHz
        Current Speed: 1600 MHz

Now whatever I do the Current Speed stays at 1600 MHz which is rather silly.

$ cat /proc/cpuinfo | grep -i mhz
cpu MHz		: 3301.000
cpu MHz		: 3301.000
cpu MHz		: 3301.000
cpu MHz		: 3301.000

Only powertop shows the real turbo frequency of 3400 MHz for each core ;-)

[Gareth Jones]

For Intel Core i3/5/7 processors, i7z is a handy tool for checking CPU speeds and behaviour: http://code.google.com/p/i7z/.

It won't be much use for other processors though.