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Why does the i7-8750H processor not work at full power?
Hello.
Clarify the situation please I bought a laptop XPS 9570 with a processor i7-8750H, which according to the specification should work at a frequency to 4.2 GHz. But when I run 3D rendering programs (similar to V-Ray ...I tested it on several different applications) where the maximum processor speed is needed, Task Manager shows that the processor runs at a frequency of only 2.9-3.15 GHz.
Is it some kind of processor feature or the laptop somehow can be configured to use the full possible processor power when rendering?
ejn63
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September 19th, 2018 09:00
Remember: 4.2 GHz is achieved ONLY with a single core active. It cannot be achieved with multiple cores running.
With more than one core active 3.9 GHz is the max.
Also bear in mind this is a very power hungry CPU (45W) -- and in a system as slim and light as the XPS, you will not be able to sustain high speed operation for very long before the system will overheat and throttle back.
We've reached a point where if you want the flat-out performance of a fast CPU, you need to sacrifice portability for it - yes, you can buy systems where the CPU will run flat-out - 17'', 10-15 pound systems with the needed heatsinks to keep the CPU cool enough. You will find that the slimmer and lighter the system, the greater the compromise in portability -- doesn't matter who made it; it's just not possible to max out the performance of this level of CPU is a sub-5 pound system.
jphughan
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September 19th, 2018 14:00
Adding just a bit to ejn63's absolutely correct answer, Intel's specs page for this CPU here indicates that the max CPU frequency is 4.1 GHz, not 4.2 GHz -- but note that that's the "Turbo Frequency". Turbo frequencies are only meant to be achieved under certain conditions in terms of how many cores are loaded, CPU temp, etc., and even then often only for bursts of time. Some systems don't have enough thermal capacity to ever achieve the max turbo frequency. By comparison, the base frequency shown on that same specs page is 2.2 GHz. THAT'S what you should expect to see on a pretty regular basis when your system is working on a CPU-intensive workload. Technically it might throttle even below that figure under certain cases, such as extreme heat (possibly due to the GPU also being worked hard), scenarios where an undersized AC adapter is connected, etc., but even a slim and light system like the XPS 15 should be able to sustain the base frequency quite consistently under most operating conditions. I haven't researched this exhaustively, but I would be surprised if there were reasonably portable laptops that could keep a CPU running consistently in its Turbo range. When I read about systems that can do that, it's usually desktop systems that have aftermarket cooling solutions, usually water cooling.
samos1111
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September 20th, 2018 04:00
In fact the CPU seems to run higher than the "base" frequency. Mind a clock may be lower also due to a core idling.
The CPU might be restricted by direct thermal throttling, if the core temperatures get near 100. The remedies are undervolt and repaste preferably with Kryonaut (you should be able to get Dell service do repaste for you - direct thermal throttling is not normal but unfortunately not uncommon with XPS due to the underdesigned cooling).
One possible limit is the short turbo time - if the CPU is loaded continuously, the short turbo time expires in probably about half a minute. After that, PL1 throttling kicks in, restricting the power to the nominal TDP of 45W, which presumably allows about 3.1 GHz with all cores loaded (you can try the Prime95 load test with 12 threads or less). Some programs load the CPU intermittently and don't get tripped by this.
Additionaly, the PL1 may get reduced to less than 45W due to "ambient" temperatures, maybe DIMM under Dell EC at 63. This is unfortunately a "standard" feature of XPS, undisclosed in the specs. The voltage regulators (VRMs) have no active cooling and can't handle long-term full load especially on both the CPU and the GPU at once, heat gradually builds up in the central area as one can see in some thermal images posted online. If you see this problem, you can try working around by padding the VRM mosfets with a thermal pad sheet "bridge" to the heatpipes, and padding the RAM and the nearby DIMM sensor to the backplate. You can also look up the more involved iunlock's mod for the 9560.
So, run HWinfo64, open Sensors and doubleclick some relevant temperatures, clocks, and package power limit, also watch throttling flags, then run your program and some load tests (Prime95, Unigine Heaven) to see what's going on.
ejn63
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September 20th, 2018 06:00
Also note that this issue isn't unique to Dell - you'll find complaints all over from Lenovo, HP, Acer, ASUS, Apple -- you name it -- anything thin and light using these CPUs.
This is a repeat of what happened last time Intel was outmatched in the performance race by AMD and began adding cores and upping clock speeds. Systems run hotter and hotter, and performance throttles as a result.
Monaco Felice
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September 20th, 2018 09:00
Many thanks to all for answers and clarifications!
Monaco Felice
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November 7th, 2018 10:00
Hello again! I have one more question on this topic.
Will there be the same problem on a Dell XPS laptop with i9 processor?
I need maximum processor performance in a compact package for working with 3D rendering programs.
Does it make sense to change the XPS with a processor i7 to i9? What will be the performance gain, given these conditions?
Thanks!
jphughan
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November 8th, 2018 09:00
You should probably look for a review of that system that was specifically configured with the i9 processor. Any thorough review will be more valuable than predictions you'll get here. But I suspect that if you need sustained fast performance rather than occasional bursts, the i9 won't make much of a difference because as you're already seeing, even the i7 can end up throttled. The fundamental issue is that asking for "maximum processor performance in a compact package" is trying to have it both ways at the same time. It's simply not realistic. Systems as thin and light as the XPS 15 can't allow H Series processors to run at maximum frequency for prolonged periods of time, especially if the GPU is also loaded. If you want to be able to do that, you'll need something larger, such as the Precision 7530 or perhaps the brand new Alienware m15.
ejn63
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November 8th, 2018 10:00
Good advice. There aren't many absolutes in the technology world, but here's one: the i9 CPU has no business being installed in any system this lightweight. Just about every one of these systems -- Dell, Apple, HP, Acer, ASUS, Lenovo, etc.) has generated the same litany of performance complaints. The sole thing the i9 will do in a system like this is give you bragging rights -- it just doesn't function well.
There is no way to properly cool a 45W CPU in a system this slim, period. It WILL throttle.
The i9 is Intel's response to competitive pressure from AMD. It just isn't a practical device for lightweight notebooks.
Diatalis
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March 2nd, 2019 12:00
i was very happy to see your answer. i have been searching this info for a few hours and came across your added info. learning about the info part of my laptop vs the advertised promise of processor speed was concerning to me. i spent a lot of money on my new laptop and was wondering why it says 2.2ghz when i bought it with specs of 3.9ghz. thank you for helping me learn more about this issue.
Zb1012
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April 22nd, 2019 06:00
What if this happens in a desktop with an i7 8700 and gtx 1070? Ive been having performance issues in my games where the cpu gets to temperatures near and even at 91 C. I have been in many tech supports and only recently did some digging and found that my parts were running hot. I complained to dell multiple times about having hot components and performance issues and didnt do anything about it and now my warranty is up. Also under full load it the cpu seems to flutter, and i dont understand why it is doing this, could you maybe help me with this issue @ejn63 ?