# Laptop CPU throttling under load even when cold and under powerlimit?



## owen10578 (Nov 18, 2016)

So I recently got this HP Spectre X360 with the "i7" 6500U in it which is a 2.5GHz base 3.1GHz boost part with 15W TDP. Now what is weird is that whenever I load it the CPU kicks to 2.9-3GHz and goes to 18W for about a few minutes and then it starts throttling down slowly until it reaches 2.1GHz drawing 9W and when it does this the CPU was only at about 80C when it still boosts and when i throttles down its at 67C so in theory it isn't hitting any limits then. But when I open throttlestop it says TDP throttle and changing any settings there doesn't do anything. What's even weirder is that if I plug in the power cord it does the boost and throttle down thing again and when it settles down already and I unplug it it does the boost and throttle down thing again. So I am at a loss here as to why this happens so if anyone can help "fix" this issue I greatly appreciate it thanks


----------



## phanbuey (Nov 18, 2016)

so i had a similar issue with alienware - laptop that would throttle the CPU under limits, and it actually did the same thing when you unplugged it. - and plugged it back in.. it turned out to be something to do with the power draw of the system and the power delivery to the components - happened particularly during games / constant load.

At first i thought the VRMs might be over heating but the more i think about it it, the more i think it was some sort of limitation.  Not sure about a solution unfortunately - i ended up having to turn off turboboost completely...  or you could try using intel XTU for additional tweaks.

It kind of sounds like they designed that machine for bursty office tasks and less for constant load....  im sure if you let it idle for a bit it goes back to normal

EDIT:  just checked on that processor_level tweak... doesnt do anything... ignore


----------



## owen10578 (Nov 18, 2016)

phanbuey said:


> so i had a similar issue with alienware - laptop that would throttle the CPU under limits, and it actually did the same thing when you unplugged it. - and plugged it back in.. it turned out to be something to do with the power draw of the system and the power delivery to the components - happened particularly during games / constant load.
> 
> At first i thought the VRMs might be over heating but the more i think about it it, the more i think it was some sort of limitation.  Not sure about a solution unfortunately - i ended up having to turn off turboboost completely... i kthink here is some setting in windows environment variables thats supposed to be able to tweak the processor_level down that may alleviate it, or you could try using intel XTU for additional tweaks.
> 
> ...



Hmm interesting. So there isn't much that I can do then? Because I tried XTU as well and it isn't doing anything. Also how it throttles is kinda weird as the CPU utilization in task manager goes down too.


----------



## phanbuey (Nov 18, 2016)

try turning off turboboost andO see if it at least stays at 2.5Ghz... if it does then it might be the same thing i had.

It was annoying as all hell - the only way i could prevent it is to limit the draw of the system.  otherwise my FPS would just tank.  It was particularly bad in overwatch.

FPS limiters will help too if you're running a game.

Basically the alienware would turbo at full power to 3.5ghz, and then would drop to 2.1 then to like 1.9 and if i kept the load up eventually would drop to 1.5.... if i limited it to 3.0Ghz using XTU it would stay there for ALOT longer... if i just turned off turbo boost all throttling would stop.

my two theories were: power delivery components overheating, when switching power sources it was using a different pathway so it would give the system some breathing room... but then back to normal OR some artificial system limitation to keep their cheap mobo from melting under extreme load which would reset upon power switch.


----------



## Komshija (Nov 18, 2016)

First thing I would do is disassembly and proper cleaning. Then I would replace thermal paste. 
Otherwise, maybe GPU or motherboard temps are higher than they should be or motherboard is receiving too much voltage. Try to adjust the voltage limits in bios (if there is such option) and turn off power saving features (first look if you have such menu in bios and then do it in the OS).


----------



## owen10578 (Nov 18, 2016)

phanbuey said:


> try turning off turboboost andO see if it at least stays at 2.5Ghz... if it does then it might be the same thing i had.
> 
> It was annoying as all hell - the only way i could prevent it is to limit the draw of the system.  otherwise my FPS would just tank.  It was particularly bad in overwatch.
> 
> ...



I see. Thanks. But how do I got about turning off turbo? From throttlestop or XTU? And yeah its basically the same symptoms as you described and I don't think its the motherboard or other components overheating as then it would trigger the BD PROCHOT signal which according to throttlestop doesn't get triggered. I even tried uninstalling all intel drivers and still the same thing happened. Pretty sure its an artificial limiter somewhere.


----------



## phanbuey (Nov 18, 2016)

owen10578 said:


> I see. Thanks. But how do I got about turning off turbo? From throttlestop or XTU? And yeah its basically the same symptoms as you described and I don't think its the motherboard or other components overheating as then it would trigger the BD PROCHOT signal which according to throttlestop doesn't get triggered. I even tried uninstalling all intel drivers and still the same thing happened. Pretty sure its an artificial limiter somewhere.



There is a setting in the bios - sometimes called c-states, sometimes they just call it turboboost depending on the vendor - I've also seen "intel dynamic thermal control".  You can also do it in xtu by unchecking a few options and/or limiting the boost multiplier to stock clocks.


----------



## owen10578 (Nov 18, 2016)

phanbuey said:


> There is a setting in the bios - sometimes called c-states, sometimes they just call it turboboost depending on the vendor - I've also seen "intel dynamic thermal control".  You can also do it in xtu by unchecking a few options and/or limiting the boost multiplier to stock clocks.



Ok thanks I'll give it a try when I get my hands on the laptop again since my parents are taking it on a holiday as of now. Anyways, I looked online and it seemed according to some other forum posts throttling was prevalent on the Skylake spectre...something fishy is going on.


----------



## unclewebb (Nov 18, 2016)

A low power U series CPU is not designed to run at full speed indefinitely.  Depending on the manufacturer, long term, it might not even run at the full Intel TDP rating.  Buying a U series CPU is a real crap shoot.  These are almost like 2 or 3 completely different CPUs in one package.  Open up the ThrottleStop TPL window and have a look at the TDP Level Limits in there.  These CPUs can automatically switch to different TDP Levels.  It can enter the low TDP Level, and it can get stuck there for an extended period of time and there is nothing that software can do about that.  Each TDP Level will usually also have a different maximum multiplier associated with it. 

Nothing really fishy.  Intel just gave individual manufacturers way too much control so a U series CPU in one device might perform at only a fraction of the speed of the exact same U CPU in a different device.  I would only buy one of these if I could use it for 24 hours and do some thorough testing before having to commit to buying it. 

Did you try running the ThrottleStop - Limit Reasons program while testing?  This should flash in red and tell you the reason for throttling.  If you try to run one of these at full load with a stress testing program like Prime95 or similar, the CPU is going to be trying to run way over the TDP limit so it will immediately start to throttle.  Limit Reasons should show some hints like PL2 limit and then PL1 limit etc.  It might also show things like the current limit being reached.

The only hope of getting more performance out of one of these is you have to reduce the CPU voltage.  The less power they draw, the faster and longer they can run at full speed before tripping one of the various limits.  The good news is that many of the Skylake based CPUs can be significantly under volted.  Next time you get your hands on this laptop, post some ThrottleStop screenshots.  There are a few minor tweaks you can do that might help the cause.  If you want reliable and steady performance, best to avoid the U CPUs.

Edit - Just for the record, CPU core temperature is rarely the limiting factor when these start to throttle.  It is mostly power related.


----------



## Ungari (Nov 18, 2016)

owen10578 said:


> I see. Thanks. But how do I got about turning off turbo? From throttlestop or XTU? And yeah its basically the same symptoms as you described and I don't think its the motherboard or other components overheating as then it would trigger the BD PROCHOT signal which according to throttlestop doesn't get triggered. I even tried uninstalling all intel drivers and still the same thing happened. Pretty sure its an artificial limiter somewhere.



Turning off C-State in the BIOS is a power saving feature and I would try this, but the Turbo clock is a separate function that can be disabled under _Intel Turbo Boost Technology_.


----------



## owen10578 (Dec 30, 2016)

unclewebb said:


> A low power U series CPU is not designed to run at full speed indefinitely.  Depending on the manufacturer, long term, it might not even run at the full Intel TDP rating.  Buying a U series CPU is a real crap shoot.  These are almost like 2 or 3 completely different CPUs in one package.  Open up the ThrottleStop TPL window and have a look at the TDP Level Limits in there.  These CPUs can automatically switch to different TDP Levels.  It can enter the low TDP Level, and it can get stuck there for an extended period of time and there is nothing that software can do about that.  Each TDP Level will usually also have a different maximum multiplier associated with it.
> 
> Nothing really fishy.  Intel just gave individual manufacturers way too much control so a U series CPU in one device might perform at only a fraction of the speed of the exact same U CPU in a different device.  I would only buy one of these if I could use it for 24 hours and do some thorough testing before having to commit to buying it.
> 
> ...



Wow. I just know all that. Sorry I just replied I only now have the laptop again. So yea I tested Throttlestop and it does show it's hitting a limiter definitely. And its not even over 80C but I think if it ran at full throttle it would go over 90C eventually even with the fan running so maybe that's why they did it? So the full speed are just short bursts. Also I haven't tried undervolting it but I'll try it now. 

Another thing that's odd to me is how it limits CPU utilization when it throttles, if I ran a stress test and look at task manager eventually the CPU graph goes from 100% to 70-80% or so when it throttles so I'm thinking it's a software thing so can I remove that limitation you think or is it not stoppable? I tried uninstalling Intel drivers and such but seems to have no effect too. Again thanks for the help. To everyone replying in this thread.


----------



## unclewebb (Dec 30, 2016)

ThrottleStop 8.40
https://www.sendspace.com/file/p6wkzr

If you run the ThrottleStop - Limit Reasons program, it will tell you exactly why your CPU is throttling.  If you are trying to run something excessive like Prime95 on a low power U CPU, Limit Reasons will show you in real time as various limits kick in and slow your CPU down.  You might see the power limits PL2 and then PL1 and you might also see the current limit or the temperature limit, etc. 







There are a pile of limits built into Intel CPUs at the hardware level and in some cases, depending on the individual manufacturer, it might not be possible to find a work around to get the kind of performance that you were hoping to get.

I would ignore what the Task Manager is showing you.  It uses the default multiplier to base the 100% point.  When your CPU starts slowing down, it shows this as a decrease in Utilization.  When Intel Turbo Boost kicks in, it will calculate the Utilization to a number beyond 100% but will then cap it at 100%.  It is not an accurate look at what a CPU is really doing.  It is about as useful as the Resource Monitor telling me that my CPU is running at 145% of its Maximum Frequency.


----------



## owen10578 (Dec 30, 2016)

unclewebb said:


> ThrottleStop 8.40
> https://www.sendspace.com/file/p6wkzr
> 
> If you run the ThrottleStop - Limit Reasons program, it will tell you exactly why your CPU is throttling.  If you are trying to run something excessive like Prime95 on a low power U CPU, Limit Reasons will show you in real time as various limits kick in and slow your CPU down.  You might see the power limits PL2 and then PL1 and you might also see the current limit or the temperature limit, etc.
> ...



Throttlestop shows PL1 limit for the CPU after running a stress test for sometime and the CPU gets to high 60s-low 70s. I think what triggers it is once the CPU gets above 80C for a while. Also I just knew Task Manager calculated utilization that way huh the more you know.

Also I've tried undervolting it in throttlestop but it doesn't seem to give a damn what throttlestop does. I can't adjust anything using throttlestop.


----------



## unclewebb (Dec 31, 2016)

When adjusting the voltage on some CPUs, you need to adjust both the CPU Core and CPU Cache equally.  Only adjusting the CPU Core voltage by itself will not do anything.  I have heard that many of the 6th Gen U CPUs can be safely undervolted by -150 mV and this can make a significant difference to heat output and battery run time.

The PL1 limit is the long term turbo power limit.  Intel recommends that this be set to the same value as the TDP.  The TDP for a Core i7-6500U is 15 Watts so PL1 is most likely set to 15.  You can open up the ThrottleStop TPL window to confirm this.

http://ark.intel.com/products/88194/Intel-Core-i7-6500U-Processor-4M-Cache-up-to-3_10-GHz



owen10578 said:


> I think what triggers it is once the CPU gets above 80C for a while.



Most throttling is power related these days and not temperature related.  A CPU can operate at the PL2 limit for a short period of time but after that, it will be throttled just enough to keep it under the long term PL1 power limit.  The more demanding the task, the quicker that the CPU will switch from PL2 to PL1.

The 6500U also has a 7.5 Watt mode that the CPU can randomly enter.  Intel calls this Configurable TDP Down.  Some laptops lock it into this mode when running on battery power.  The ThrottleStop TPL window will show you what TDP Levels your CPU supports.


----------

