Gentoo and i7 sandy bridge with turbo boost

[kbzium]

Hello,

my cpu is i7 2600 3.4GHz stock, max 4.2Ghz with turbo boost (4.2GHz - 1core, 4.0 2cores, 3.9-all cores).

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
returns 3401000

Does it mean that my cpu run at that speed or, what i think is right, that gentoo only reports that turbo boost was on (that 1) and i cannot determine real frequency. I'm asking to be sure, that I'm getting all that i can from this rig.

Thanks!

[gentoo_ram]

I'm not sure you can directly see the turbo boost numbers. Do you have the CPU frequency stuff turned on in the kernel? If so, you can get information for each "CPU" in the system.

[kbzium]

Ok, so let's assume that turbo boost works fine. But: what about processor states? Do idling cores turn off preventing heat & power consumption? Again, how to check it?

[megaflow]

the app app-benchmarks/i7z will give u good info
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Dell System XPS L702X/0XN71K,Intel(R) Core(TM) i7-2720QM

[kimmie]

sys-power/powertop will tell you as well (the 2.0 version will give you more info)

[kbzium]

[kimmie]

Enabling AC97 power saving will probably save power, the downside is that some apps may not wake the hardware correctly (in which case you'll get no sound). Also, depending on your hardware, you might get annoying loud clicks when the hardware wakes. The only way to know is to give it a try.

If you want detailed stats from powertop, enable the CONFIG options it suggests. It won't hurt. Also, it looks like you're running powertop 1.0? Try 2.0 (it's in testing but it should work fine on a stable system).

I don't know i7z, but it seems to be complaining it can't access model specific registers. Try enabling the CONFIG_X86_MSR for your kernel (it's in processor type and features).

[kbzium]

Weird, but the system doesn't seem to use more thatn 25% of cpu power anytime, even during kernel compilation: is there any benchmark that could prove me wrong? Maybe haven? I downloaded haven.run but i don't really know how to run it... permission denied always.

[kimmie]

kernel compilation won't use > 1 processor unless you tell it to.. try using "make -j8" to build the kernel.

Same goes for portage, good settings to maximise your machine usage for emerge in make.conf are:

[kbzium]

It seems i've made it already. But are the other settings okay? It's really slow.

/etc/make.conf

[kimmie]

[JanR]

Hi,

first: Intel CPUs offer Turbo boost hidden as the highest P-State. In your case 3400 (I leave out the remaining 3 Zeros in this post) is 3.4 GHz - your default frequency in no-turbo-mode. All lower frequencies are the lower P-states. The remaining one is max+1 MHz, in your case 3401. This is "enable turbo". It does NOT tell you a which frequency it will run but it enables turbo and let the hardware decide.

By selecting this p-state you enable turbo (which seems to be the case for you).

Second: There is a tool called "turbostat" hidden in the tools-directory of the Linux kernel. Build this and you will see detailled statistics on turbo (updated every 10 s). Let it run and start load with different degrees of parallelism - you will see the individual states. Keep in mind that the highest state is only selected if really nothing else is running - this is nearly never the case with modern GUIs. Disable X and try it on console - this will give you much higher boost.

As your CPU seems to be overclocked (normal max turbo state for 2600K is 3.8 GHz, not 4.2) I'm not sure what turbostat will show.

Third: There is a great utility called "mhz" belonging to the very old "lmbench" (dropped from portage years ago but you can just download and build it). This one does not try to read some MSR etc. but runs a test that quite successful figures out the real frequency of the CPU. From my experience, it worked on every machine I tried (except P4 Northwood, here you get two times the frequency which is not that wrong as Northwood runs the ALU at that speed). On a multi-core system, it is better to taskset it to one core.

Example:

[kbzium]

Thank you, you made it a lot clearer. But what about voltages? Does it also let processor (or bios) decide? I don't want my i7 running at 1.2V at 1600MHz, cause it normally runs at 0.9V then. That would be my last concern, if my "wakeups-per-second" are good too.

Moreover, do you happen to know what kernel options should I enable in order to fully monitor my CPU yet not let it be destroyed anyhow? Now i cannot display detailed things like temperature and so on.

// edit:
Kernel compilation still uses only 1 tread/core. up to 15%... Any ideas? I've changed those two options.

[JanR]

Hi,