Undervolting Skylake-U Imrpoves Performance During CPU+GPU Loads

firewolfsm

Golden Member
Oct 16, 2005
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So I played around with my new XPS 13 (i5-6200U) and Intel's XTU utility while running Furmark and Prime95. During this load, of the 15W available TDT, the GPU used 10W and the CPU only 3W, I guess the remaining 2W are for cache + memory controller. Through it, the GPU ran at 950MHz but the CPU ran at only 1.2GHz due to TDP throttling.

As I gradually undervolted the CPU from -0 mV (dynamic offset) to -90 mV the frequency slowly ramped up to 1.5GHz. Undervolting the GPU to -60 mV brought the frequency up to 1.8GHz by lower the GPU's portion of TDP from 10W to 8W, leaving 2 extra watts for the CPU. The GPU seems perfectly stable at this level, but the CPU crashes past -90 mV.

This will dramatically boost FPS in any game which is CPU bound, but will not affect CPU or GPU loads alone, except to save battery life.

Any other results? If anyone has a Skylake laptop, try undervolting and see how far it goes. Also, I don't think it's possible, but if there's any way to overclock the BCLK on this processor I'd love to hear it, even if I only get from 100 -> 103MHz, that would help.
 

Ken g6

Programming Moderator, Elite Member
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Cool ( literally) test result. Thanks for trying that.
 

dark zero

Platinum Member
Jun 2, 2015
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I wonder if Carrizo FX will have the same problem.... look at Kaveri... and now at Intel U tier... seems that OEM's screws a lot.
 
Aug 11, 2008
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That is a very heavy load. I wonder how the TDP would split up in a game.

Looks like 15 watt TDP is still not enough to fully utilize both cpu and gpu. Disappointing actually. I would have thought the cpu could at least maintain base clocks under heavy gpu load at factory settings.
 

Burpo

Diamond Member
Sep 10, 2013
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Not all OEM's factory settings will be the same. HP's have historically been faster than Dell on laptops with same config.
 

SirCanealot

Member
Jan 12, 2013
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XTU is awesome. You can use it on Surface Pro 3s to actually get some decent performance out of them.

My girlfriend's Haswell laptop (i7 4702mq and 760m) gets to 90/80 degrees for CPU/GPU and is pretty noisy, but with a -75mv undervolt on the CPU it drops it by about 5-10 degrees for both :) (apparently most chips can go past -75 but I always get the crappy ones)

Remember: As long as you undervolt properly (and don't corrupt your software), undervolting is one of the only things you can do to increase performance/battery life for FREE. Enjoy :)
 

coercitiv

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Jan 24, 2014
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As I gradually undervolted the CPU from -0 mV (dynamic offset) to -90 mV the frequency slowly ramped up to 1.5GHz. Undervolting the GPU to -60 mV brought the frequency up to 1.8GHz by lower the GPU's portion of TDP from 10W to 8W, leaving 2 extra watts for the CPU. The GPU seems perfectly stable at this level, but the CPU crashes past -90 mV.
I would be very careful going past -60mV undervolt, as the system might seem stable under (prolonged) load, but may not be stable at specific temperature/load points. In other words, one might perform extensive tests with the CPU at say -60mV offset and conclude it's stable, only to find it crash after a cold start under seemingly light load.

This is particularly true for Haswell systems, so your mileage may vary more in Skylake, since many parameters have changed.

It is however, very good news to hear about a -90mV undervolt on Skylake U, lots of potential to be untapped.
 

Yuriman

Diamond Member
Jun 25, 2004
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Apples to oranges, but I've been running a -0.11v for around 3 months now on my Ivy Bridge and haven't run into any stability problems. Voltage will vary from motherboard to motherboard, and even if all CPUs need the same operating voltage at various frequencies (which clearly isn't true), what works with one CPU/board combo will not necessarily work for another.
 

SirCanealot

Member
Jan 12, 2013
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I would be very careful going past -60mV undervolt, as the system might seem stable under (prolonged) load, but may not be stable at specific temperature/load points. In other words, one might perform extensive tests with the CPU at say -60mV offset and conclude it's stable, only to find it crash after a cold start under seemingly light load.
This is very true. However, luckily XTU isn't stupid. Actually it's oversensitive. If you even sneeze in the direction of the machine wrong, XTU resets the settings.

Which is good for stability, but annoying when your GF asks why the laptop is running hot and you realise XTU has reset itself again...

But yeah, all you can do is go slowly and see if you crash under different circumstances.
 

cytg111

Lifer
Mar 17, 2008
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That is a very heavy load. I wonder how the TDP would split up in a game.

Looks like 15 watt TDP is still not enough to fully utilize both cpu and gpu. Disappointing actually. I would have thought the cpu could at least maintain base clocks under heavy gpu load at factory settings.
Yea, I'd like to see the same test on a SP4
 

dark zero

Platinum Member
Jun 2, 2015
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I guess it's time to make a thread about Intel Extreme Utility.... is interesting since I boost my processor Core i7 4702 MQ up to 3.4 Ghz Turbo (one core) and 3.0 Ghz Multi
 

pooptastic

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Oct 18, 2015
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It's been a while, but i thought laptops didn't have a full bios that allows you to modify or overclock it at all?

I had an old Dell, and later a P4 Alienware and i don't remember having access to anything like that. I figured OEM's had a limited bios they replaced it with so you don't overclock or do anything yourself.

(edit: Intel Extreme Utility apparently bypasses this. cool beans. Doesn't fully work on my 2011 system though...)
 
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dark zero

Platinum Member
Jun 2, 2015
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It's been a while, but i thought laptops didn't have a full bios that allows you to modify or overclock it at all?

I had an old Dell, and later a P4 Alienware and i don't remember having access to anything like that. I figured OEM's had a limited bios they replaced it with so you don't overclock or do anything yourself.
However Intel XTU seems that helps at least by 10% the performance of the chi

Not all OEM's factory settings will be the same. HP's have historically been faster than Dell on laptops with same config.
Except in AMD... they always screw AMD
 
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NTMBK

Diamond Member
Nov 14, 2011
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You should try turning off Hyperthreading, too- I've seen that free up a little GPU headroom on my tablet.
 

mikk

Diamond Member
May 15, 2012
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Looks like 15 watt TDP is still not enough to fully utilize both cpu and gpu. Disappointing actually. I would have thought the cpu could at least maintain base clocks under heavy gpu load at factory settings.

Did you really expect full speed with Furmark+Prime95 at the same time on a 15W ULV? You can't even make assumptions for games based on that. To me 950 Mhz for the GPU is better than I would expect. It's the maximum 3d turbo for i5-6200U.
 

firewolfsm

Golden Member
Oct 16, 2005
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Yes, 950MHz is pretty good, being the max sustained frequency (1GHz for short durations). I think Intel intentionally prioritizes GPU when both are loaded, which would be better for almost any GPU-bound task.

And yes, after undervolting, I did see instability at idle and the computer crashed. Actually rebooted and crashed 3 times before XTU caught on and reset itself.

I guess at 15W, the chip is definitely limited under full, artificial loads, but at 1.8GHz after undervolting, it's not too far off from full speeds. I would guess that 18W would suffice while undervolted, and 23W under normal.
 

firewolfsm

Golden Member
Oct 16, 2005
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Just want to add an update:

I had to replace my laptop after the WiFi card gave out. Oddly, the replacement has better performance at equal voltages. This one sustained 1.5GHz on the GPU at stock voltage under the same task, rather than 1.2GHz, and increased to 2.2GHz with the same voltage reductions.

As this is a full 10% ference, I think this has some implications for how sites like anandtech review laptops for performance and battery life.
 

Anthony Chen

Junior Member
Aug 15, 2016
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Normally my laptop's i5/6200U Skylake Cpu functions well at 2.7Ghz at full load. The package uses 15watts. Putting on an iGPU load brings the pot 18watts temporarily, but the CPU is soon clocked down to 2.1GHz to reduce the Power consumption of the CPU.

With Intel XTU I managed to under volt my laptop CPU with an off set of -100mV Power Consumption on a CPU load has dropped to 11.7W, which should allow for a higher CPU/GPU clock speed when both are under load
 

superstition

Platinum Member
Feb 2, 2008
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firewolfsm said:
I think this has some implications for how sites like anandtech review laptops for performance and battery life.
It could be silicon lottery.

It could be differences in the thermal paste application.

It could be both.
 

linkgoron

Platinum Member
Mar 9, 2005
2,072
507
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While it seems this thread is a necro, I've also had success with undervolting my 6700HQ by -150mv on my XPS 15. Increasing (decreasing?) the undervolt to 160/170mv caused crashes and problems. I also undervolted the iGPU by -100mv, although it has a discrete 960m so I'm not sure how much it matters. I know of others on notebookreview who undervolted by 160/170.
 

Aquacelot

Junior Member
Mar 3, 2017
1
0
1
So I played around with my new XPS 13 (i5-6200U) and Intel's XTU utility while running Furmark and Prime95. During this load, of the 15W available TDT, the GPU used 10W and the CPU only 3W, I guess the remaining 2W are for cache + memory controller. Through it, the GPU ran at 950MHz but the CPU ran at only 1.2GHz due to TDP throttling.

As I gradually undervolted the CPU from -0 mV (dynamic offset) to -90 mV the frequency slowly ramped up to 1.5GHz. Undervolting the GPU to -60 mV brought the frequency up to 1.8GHz by lower the GPU's portion of TDP from 10W to 8W, leaving 2 extra watts for the CPU. The GPU seems perfectly stable at this level, but the CPU crashes past -90 mV.

This will dramatically boost FPS in any game which is CPU bound, but will not affect CPU or GPU loads alone, except to save battery life.

Any other results? If anyone has a Skylake laptop, try undervolting and see how far it goes. Also, I don't think it's possible, but if there's any way to overclock the BCLK on this processor I'd love to hear it, even if I only get from 100 -> 103MHz, that would help.
I have undervolted my i7 6500U by -50 mV and it works fine and I am wondering if it would work to undervolt mine to the same as your i5 6200U.
 

ZGR

Golden Member
Oct 26, 2012
1,958
486
136
I don't advise gaming on a laptop unless turbo boost is off. Intel Turbo Boost is far too aggressive and steals thermal headroom from what is important in a game; the GPU.

My i7 3720qm (3.4 GHz all cores) runs far too hot and consumes too much power in a game with turbo on. Disabling turbo lets the GPU have most of the available headroom.

I would suggest setting the max processor state to 95% in power settings and keep the undervolt. This will provide a massive amount of thermal headroom as well as keeping the fans quiet.

If you need to fine tune the frequency, check out Throttestop on the notebookcheck forums. I use it to dial in CPU frequency to the minimum that is required to saturate the GPU. In many games even 2.0 GHz is plenty and lets the CPU and GPU run significantly cooler.

Letting Turbo Boost have its own way in a CPU and GPU intensive game usually forces the CPU to throttle as it is running at far too high a frequency with not enough thermal headroom.
 

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