Fix Throttling CPU on Lenovo Flex 5

 lift the laptop a bit, to keep the air vents with good air flow

disabled the "Intellegent Cooling", turned off the smart cooling feature on Lenovo Vantage. I'd say to install Vantage and see if you can disable the feature.

undervolt your CPU: https://www.notebookcheck.net/Intel-Extreme-Tuning-Utility-XTU-Undervolting-Guide.272120.0.html, and as you probably know, you can undervolt your GPU with MSI Afterburner.

Intel XTU it actually records and tells you when thermal throttling has occurred, no guessing. 

From this, I realized that the integrated graphic, for some reason, took over during gameplay, and this would trigger power limit throttling, reducing the frequency of the CPU to below 1GHz. So I went to device manager, updated the driver for Intel UHD, then set the game to specifically run on the gtx in the Nvidia control panel. 

I've also had lots of issues with the thermal throttling on my Lenovo Yoga 730 16 ram 1050. I tried to undervolt the CPU by almost 200 mv on throttlestop. It seemed to help out a bit. I don't know if it is safe to lower it any more.

 i7 8550u. I decided to undervolt it to lower max temperatures and get longer battery life. What I didn't realize was that it would give me much better performance as well. I used Throttlestop to undervolt my CPU and CPU cache, to -95.7mv. 

I was able to reach -100mv semi-stable, (-110mv crashed immediately) but my machine froze and I don't feel like going through all the trouble of testing it more thoroughly and potentially losing my work for 5mv. So I left it at -95.7mv.

I heard that leaving XTU in the background can be detrimental to performance, but yes, it's mostly personal preference.

I'm just undervolting now and my first try (-80mV) has given me just over 600 score on Cinebench (4 runs so far). Temps are consistently 75 C or below, too.

After some iteration, I'm settled at about -110mV (-120mV seemed okay but the second Cinebench run crashed stuff, so I backed off). Running Prime95 now, the final Cinebench score at -110mV was 621. Pretty good, I'd say.

 settled on the following with my Spectre 15 x360 with Coffee Lake i7-8550u: -154.3mv on the CPU Core -104.5mv on the CPU Cache -44.9mv on the Intel GPU

The resulting boost in multicore performance is around 17%.

My best multicore cinebench R15 score with these undervolts is 638, up from 530~

ou want the Core and Cache voltage to be the same. I am unsure how dangerous it is for them to be different, but I would not advise keeping it the way you have it in the least...

 an app called ThrottleStop. No tweaks whatsoever, just run it and the i5-8250U will behave like an i5-8250U should, clocking at 2.8-3.4Ghz the first few minutes and stays at 2.2-2.3Ghz under sustained loads. The temperature does noticeably increase at 70 degrees C average under 100% load compared to 60 ish degrees C average at 1.6Ghz.

You'll want to undervolt your CPU and enable intel Speedstep and set the value more towards power saving (around 145 and up to 225). I've got mine at around -100mV undervolt and Speedstep value set at 156. It is now occasionally boosting around 3.0-3.4Ghz under light load, 2.6-2.8Ghz under moderate load, and 2.2Ghz under full, sustained, load with highest recorded temperature of around 76-84 degrees C under full GPU load+moderate CPU load.

Undervolting your CPU and lowering the SpeedShift value in ThrottleStop. You can get 3.4Ghz at all times on all core with this but it will get really hot and drains battery really fast. Even with my preffered value at 156-164, the battery still drains relatively quick.

If I may add, I find that adjusting the speedshift value has the most impact on CPU clocks, 156 being the sweet spot for mine (lower speed shift value = higher clocks). Before enabling the Speedshift option, you have to click 'TPL' then tick 'Speedshift' as well as 'Enable Speedshift when ThrottleStop starts' as shown below.

If you have the time, I'd also recommend downvolting the CPU to keep temperatures down. 

I've also found it basically impossible, even with throttlestop, to get above 15W for prolonged usage. This is on the i7-8550u 720s 

even with throttlestop it will not go over 15 watts of usage. I was able to undervolt however and that did increase my clock speed from the base 1.6Ghz to a much better 2.3Ghz but I still would like to get the full output if possible. Sadly the bios is locked down so hard that it is not possible to increase the turbo boost length or increase power output during normal operation. 

I noticed that while running these benchmark comparisons the Lenovo never got above 55C which is very strange as it is a small laptop and the cooling cant be that great. Yet the other laptop was hitting 90C which is hot yes but when a benchmark gets nearly 100% better results it makes perfect sense. So obviously the Lenovo had to be throttling somehow but I couldnt quite figure out why because the thermals had more than enough headroom and it was on AC power with max performance setting. So I started looking in to what is happening further. After some diggin I realize that the 3.4Ghz boost clock was only being used for 28 seconds at a highest 25 watts then throttling down to the 15 watt TDP. Where as the other laptop was keeping 30 watts steady as long as the CPU was under 95C. This translated into higher temps but EXTREMELY higher performance as well. The boost and base clocks are so far apart that the performance is really degraded if not allowed the extra power.

However please be very cautious about this laptop. Lenovo does not have a good cooling solution and their "fix" is to severely Power Limit Throttle, even beyond reasonable. After about one or two minutes of 3.7Gz performance, the clock speeds go down and stay at 2.5GHz, even though CPU temps are 60C and power drain is 15W.

Sorry but I think you don't understand how ULV CPUs work. Many ULV CPUs have Power Limit 1 of 15W. This means that after a short turbo run (usually about 28 seconds if there's no thermal throttling), PL2 will stop and PL1 will kick in. This is VERY NORMAL. This doesn't apply to this model only, almost every laptop with KBL-R have the same behaviour. You can check out my Aspire 5 review to see how to tune KBL-R ULV.