Undervolting the i7-720qm

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luminous
Posts: 4
Joined: Mon 4. Jan 2010, 00:39

Undervolting the i7-720qm

Post by luminous » Mon 4. Jan 2010, 00:59

Hi. I thought I'd ask if anyone has undervolted a mobile i7 processor before I try it myself. I haven't found anyone on google claiming to have undervolted this processor and I'm wondering if it's at all possible... My dell i7 laptop sure would be nicer a few degrees off. :P

the-fallen
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Re: Undervolting the i7-720qm

Post by the-fallen » Mon 4. Jan 2010, 17:01

Hi,

you are the first one I know (because you are the first who asked).
In theory they should work.

If you are going to try it I would be glad to see the results. If there are any problems please let me know so maybe I can fix them before I release the next preview-version of the upcomping 0.4 release.

luminous
Posts: 4
Joined: Mon 4. Jan 2010, 00:39

Re: Undervolting the i7-720qm

Post by luminous » Fri 8. Jan 2010, 18:03

Now I have installed the phc-patched kernel, which took some time because of a bug in wubi that broke grub so I couldn't boot. If anyone with wubi is going to update the kernel before this bug is fixed, there's a patch that fixes the problem here.

I have tried to play around with the values in phc_vids a bit and it seems that undervolting is working. I can change the vids and it shows up in ./read_msr.py --readmsr. There seems to be some bugs though. This is the contents of some of the phc-files:

phc_fids: "0 0 0 0 0 0 0"
phc_default_vids: "13 12 11 10 9 8 7 "
scaling_available_frequencies: "1597000 1596000 1463000 1330000 1197000 1064000 931000 "
scaling_available_governors: "conservative ondemand userspace powersave performance "
scaling_driver: "acpi-cpufreq"
scaling_setspeed: "<unsupported>"

The system shows cpu0 up to cpu7, and if I only change phc_vids for cpu0, it doesn't change automatically for the other cores as I read it would do with core2 processors? Edit: the file contents doesn't change but the vid:s the other core's are using seems to be the same anyway.

I guess that phc_fids shouldn't be only zeros?

There also seems to be some problem with the "CPU Frequency Scaling Monitor 2.28.0" gnu widget that I use. I haven't experimented so much yet but right now it doesn't affect the values at all in the scaling_cur_freq file and scaling_governor files when I change the scaling or governor in the graphical widget, although I think it worked earlier today, hmm...

A first report, I'm almost surprised I got this far as I'm kind of a linux newbie. :P Thanks for the nice software anyway.
Last edited by luminous on Sat 9. Jan 2010, 01:52, edited 1 time in total.

luminous
Posts: 4
Joined: Mon 4. Jan 2010, 00:39

Re: Undervolting the i7-720qm

Post by luminous » Sat 9. Jan 2010, 01:50

Frequency scaling monitor began working again, here's some results where I stressed all cores to 100% with cpuBurn:

Code: Select all

Freq	      Stable VID	   Temp	    Original Temp
931000	    7
1064000	   7		         60	      64
1197000      7		         62
1330000      7		         63
1463000      7		         64
1596000      8		         66	      80
Unfortunately it seems the processor refuses to step down to a VID below 7 even if I set the values in phc_vids lower, so at frequency 931000 it is stuck with the original setting. At 1596000 though there's a really nice 14 degree (c) difference.

The output of read_msr is a little bit confusing. Often "current VID" tracks the value in phc_vids quite well, but it often fluctuates a bit and sometimes different cores has different values. And "target VID" sounds like it should track the value in phc_vids for the currently set frequency, but most often it's some other, lower, value. I'm not entirely sure that the cpu is really running all the time at the frequency it is supposed to.

the-fallen
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Re: Undervolting the i7-720qm

Post by the-fallen » Sat 9. Jan 2010, 17:53

Thank you for this report.

I would like to get some more data from you as soon as I read some documents about that CPU. It's strange that the phc_vids - file is containing zeros.

luminous
Posts: 4
Joined: Mon 4. Jan 2010, 00:39

Re: Undervolting the i7-720qm

Post by luminous » Sat 9. Jan 2010, 19:56

Sure, I'll keep an eye on this thread!

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