1 Rookie
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5867
August 31st, 2021 23:00
XPS 8940, 11th Gen CPU power limited
Just a little rant about how stupid the Dell BIOS is. Their bios by default limits all non k cpu to 65w. But CPUs like the i5-11400 (the one I have) draws way more than that. Because of that when it's hit with a heavy multi-thread application its runs about 50% of the performance that it's supposed to. I just hope they unlock all 11th gen non k to upto 95W since the motherboard supports it.
bertro514
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363 Posts
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September 1st, 2021 10:00
@NeerajSunil what you're describing sounds like normal Intel TurboBoost behavior. I won't bore you with all the technical details, but basically the CPU is allowed to go over its advertised wattage (65W) for a limited period of time (about 30 sec), after which it's pulled back down to 65 for a while, and then allowed to boost again and so on. If you install a free app like ThrottleStop or Intel XTU, you'll see those limits (called PL1 and PL2, the duration is called "tau"). I recommend ThrottleStop over XTU, as it has way more features and allows more control.
The good news is that you can bypass those limits and allow your CPU to boost indefinitely, as long as you upgrade your cooling to keep the temps under control (otherwise, it will thermal throttle when it gets close to 100 degrees). ThrottleStop can save the day again. You can change the power limit to as high as 250W and the duration to a few million seconds (which basically means forever).
Here are the settings for my 10900 nonK. After doing this, it boosts to over 200W and stays there for as long as the benchmarks are running. It does get hot though, so I've only done this after upgrading the cooler from the default Dell "pancake" cooler to a good quality Noctua tower cooler.
Note: if you notice that the increased power settings are not "sticking", this may be due to a BIOS limitation imposed by Intel to all manufacturers last year. The good news is that you can remove that limitation too with a bit of patience and care (warning: this involves editing raw BIOS code. do this only if you're confident you know what you're doing!). Instructions here Bonus: this BIOS mod will also unlock the ability to undervolt your CPU, which will keep it cooler without losing any performance.
Vic384
4 Operator
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3.2K Posts
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September 1st, 2021 06:00
Dell BIOS limited support of K CPUs goes pretty far in the XPS desktop series. I don't know why Dell even offers the K CPU as an option given its historically limited BIOS support. My recommendation is if you are interested in fully using the capabilities of the K CPU you should consider a different motherboard/system.
XPS_Man
5 Practitioner
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2.4K Posts
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September 1st, 2021 08:00
My assumption is they Buy them in Bulk so they get both K and non K in same Price.
Than they charge customers additional 50 US $ for K version.
If they don't limit the CPU (by intention) no one purchases K version.
My Suggestion why even release a high end XPS with non K version
redxps630
9 Legend
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15.2K Posts
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September 1st, 2021 09:00
$50 more for -k cpu which is almost always a better binned cpu than non-k of same model number otherwise. The -k is a premium fancy choice in silicon lottery. It has a higher base frequency.
Dell charges additional $50 for the whole -k package in 7090 presumably including copper heatsink upgrade.
OP’s i5-11400 probably comes with the low end aluminum heatsink. If all 6 cores 12 threads are used temp might run high and throttle the cpu. Question: is the reported 50% reduction in performance due to built in Intel protective mechanism to down clock when it senses throttle or Dell bios, or are the two the same thing? If one upgrades to a better heatsink would it ameliorate the issue?
redxps630
9 Legend
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15.2K Posts
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September 1st, 2021 10:00
That is cool stuff (and “not for the faint of heart”).
I have used throttlestop on a Dell Inspiron laptop running a 6th gen pentium dual core cpu which made a big difference. It kept the cpu run at 2 ghz instead of 300 MHz. Fan was never loud. Before throttlestop the laptop was much slower than 13 year old core 2 duo desktop.
NeerajSunil
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3 Posts
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September 1st, 2021 17:00
I have the 500W PSU
NeerajSunil
1 Rookie
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September 1st, 2021 17:00
You are amazing. Yes you're right I tried with the intel XTU, but will throttle stop I was able to allow my CPU to reach the PL limits properly. Before my CPU was at 70 degrees and it wouldn't use more power. But after following your settings I was able to allow my CPU to draw more than 65W for short bursts and sustain more than 65W if the temperature allows. Thank you very much man this is a great solution.
RoHe
10 Elder
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45.2K Posts
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September 1st, 2021 17:00
The PSU in this PC with the i5-11400 is probably 360W.
If they let it go up to 95W, will you need the bigger 500W PSU, like they put in XPS 8940 systems with an i9 CPU?
bertro514
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363 Posts
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September 1st, 2021 18:00
Then you should be more than fine. I have a i9 10900 + RTX3070 and the 500 is totally fine, as I never have a real-world scenario where both CPU and GPU are maxed out. When I play games or mine, the GPU goes up to 150-210W, but the CPU usage stays down. Conversely, if I run any CPU-intensive apps, they usually don't use much GPU, so the CPU has room to draw 200W+ without issue.