# 7840U CPU Power efficiency testing

**URL:** <https://community.frame.work/t/7840u-cpu-power-efficiency-testing/40974>\
**Category:** Framework Laptop 13\
**Created:** [November 27, 2023, 9:06pm UTC](https://community.frame.work/t/7840u-cpu-power-efficiency-testing/40974 "2023-11-27T21:06:48Z")\
**Posts on this page:** 1\
**Showing post:** 1

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**Author:** ![Adrian\_Joachim](https://sea1.discourse-cdn.com/flex001/user_avatar/community.frame.work/adrian_joachim/32/9949_2.png) [@Adrian\_Joachim](https://community.frame.work/u/Adrian_Joachim)\
**Post date:** [November 27, 2023, 9:06pm UTC](https://community.frame.work/t/7840u-cpu-power-efficiency-testing/40974/1 "2023-11-27T21:06:48Z")

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Since I have somewhat working ryzenadj that lets me temporarily set power limits and somewhat working ectool that lets me temporarily set fan-speeds I got curious and mapped the power/performance curve in cinebench r15. Not sure how useful this is but it is definitely interesting.

The test-setup is my unmodified amd framework 13 with the 7840u and 64GB of 5600 memory. It’s running the latest arch with a pretty light sway setup. Test conditions are:

- Plugged into 100W power supply
- tlp (stock settings) in ac mode (battery mode distorts results because it seems to power limit to 10w for the first couple seconds before limiting to the set power limit)
- Fan fixed to max (bit under 7k rpm)
- Cinebench R15 running in wine
- Power limit set using ryzenadj (both long and short)
- Achived power-limit checked using ryzenadj -i (seems to be pretty accurate from some cross testing with battery draw)

Here are the results for multicore:

 ![image](https://us1.discourse-cdn.com/flex001/uploads/framework3/original/3X/5/3/532d0202a7f47eb309e0d47b050d9d78f3d91f8c.png)

And here for singlecore:

 ![image](https://us1.discourse-cdn.com/flex001/uploads/framework3/original/3X/c/2/c2a06046960f6178ce06de9a75c0cb680f0fb6dd.png)

Some observations:

- Well first of all I am amazed by the efficiency and performance in general
- Multicore won’t go lower than 6.8W no matter how low the limit is set
- Can’t set a power limit above 43W even if I am able to cool it, though efficiency is taking a dive at that point anyway.
- The anomaly at 7W singlecore is weirdly reproducible
- The fan at full blast uses almost 2W of power
- The fan is also a lot less loud at full blast than I was lead to believe by some people here
- Even the completely kneecapped 5W power limit running multicore at 6.8W is still the performance level of my good old x260 (liquid metal, undervolt and all)
- At 10W it is easily beating my t480s running at around 30W (this too undervolted and with liquid metal and thermal throttling all the way)
- At 25-30W we are leaving my huge and heavy work laptop (Precision 7560) even with all the power sliders turned way up in the dust (no liquid metal or undervolts on that one XD)

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