Intel Turbo Boost not working?

[delbyblue]

My laptop (with Kubuntu 9.10 and Windows 7 dual boot) has a Intel Core i7 720QM and it has Turbo Boost technology to increase a single core speed up to 2,8 Ghz. The problem is this technology seems to do not work at all under Kubuntu, but work under Windows.
I have ran following command to max out single-thread CPU usage and test this technology

cat /dev/urandom > /dev/null

but my CPU frequency never reach more then 1,6 Ghz, which is Core i7 720QM normal frequency.
TO know my cores working frequency i use

cat /proc/cpuinfo | grep -i mhz

Anybody know why Turbo Boost technology isn't working or what can i do to fix it? I haven't found any issue (except one, but doesn't look like the same problem) searching around web.

[rdelcueto]

Hi Delbyblue,
I just got an ASUS G51J, it is also equipped with an Intel Core i7 720QM @ 1.6Ghz - 2.8Ghz (w/TB). I've been messing around doing some benchmarks and I have as well noticed that the Turbo Boost feature is not working under Linux.

I already browse quite a few articles and forum posts, and first of all, there is support for Core i7 processors including Turbo Boost under recent kernels, and apparently it works for some Desktop users.

One of the things that I learned is that the CPU frequencies showned @ {/proc/cpuinfo, /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies, etc}, obviously do not include the Turbo Boost available frequencies. It can be misleading, yet there are two highest frequencies that differ only by 1Mhz, the highest of them refers to the highest cpu p-state, in which Turbo Boost should kick in if needed. Yet I've experience that it never goes beyond the fixed 1.6Ghz clock.

To my surprise I think I managed to get Turbo Boost working when I disabled entirely ACPI support under the kernel boot options ( acpi=off ). I did some benchmarks using single threaded applications, and I witness a ~200% speedup when turning off ACPI support. Of course this is not a solution, since disabling ACPI implies loosing ALL power management (p-states, c-states, thermal CPU and fan control), together with hyperthreading, plus in my case I could only access one of the four cores. Yet this pin-points the problem is some way. I tried different ACPI settings, but just by disabling everything I got to see higher clock speeds than the fixed 1.6Ghz. I say there is something broken on the ACPI support with our notebooks.

That's all I can say about the problem, I haven't found any way to fix it. =(
Please keep any updates posted.

P.S. This are the only informative sites I found, specificly about Turbo Boost on Linux:
http://kbase.redhat.com/faq/docs/DOC-17124
http://kolbusa.livejournal.com/71066.html

[delbyblue]

That give me the confirmation i needed. Thanks!

I say there is something broken on the ACPI support with our notebooks.

I'm thinking the same: this isn't the only ACPI-related issue that i found with my notebook.

[rusi_pathan]

Turbo boost is the Intel buzzword for simple overclocking. Technically you should be able to disable turbo boost in BIOS and overclock to 2.8 GHz as long as the airflow around the CPU is not too restrictive.

Just keep an eye on the temp and increase it in steps.

[rdelcueto]

Turbo boost is the Intel buzzword for simple overclocking.

Not quite, there's a small detail which makes a whole difference. Turbo boost is an adaptive per core overclock. This makes Turbo Boost an excellent power saving/perfomance enhancement, specially in laptops, which is my case.

Technically you should be able to disable turbo boost in BIOS and overclock to 2.8 GHz as long as the airflow around the CPU is not too restrictive.

The chip won't handle an overall 2.8Ghz clock. This overclock will only work when all cores except one, are idling. Turbo Boost is not a boolean overclock (ON/OFF), it has different "states", which are basically a range of multipliers. The chip will adapt to the highest stable setting, depending on the core usage.

That's when Turbo Boost makes it's magic, and makes the chip incredibly fast in single threaded scenarios, while being able to adapt to slower per core clocks (1.6-2.8Ghz range) for highly threaded scenarios.

Plus, in my laptop's BIOS I can't enable/disable Turbo boost, nor overclock the CPU.

[rdelcueto]

http://bugzilla.kernel.org/show_bug.cgi?id=15064