The Intel Core i9-9900K at 95W: Fixing The Power for SFF
by Ian Cutress on November 29, 2018 8:00 AM ESTCore i9-9900K in Small Form Factors
Even with all the hullabaloo surrounding how Intel defines TDP and what values the company should actually be advertising for the power consumption of its processors, the simple fact is that processors generate thermal energy when they run. Sometimes it’s a small amount, and sometimes it’s a lot, but in every case that thermal energy has to be managed, either by the box cooler, some super extreme water chiller loop, or by a super massive fanless heatsink. In order to maintain performance, the thermal solution also has to be suitable for the environment at hand.
Nothing proves more channeling than designing a system for something small, and still maintaining high levels of performance. There are tradeoffs – performance for noise, or silence for performance. One way to manage this is through configuring the turbo and power values of the system in the firmware, and it is this method that OEMs use for laptops and mini-PCs.
Some Performance Loss, But More Efficient
The performance that Intel guarantees is the one on the box: the base frequency at the sustained TDP. For system integrators or builders, this gives a simple comparison point, and when we set our power consumption limits for the Core i9-9900K, this is what we saw at full load: 95W gave 3.6 GHz at 7-8 core load.
Losing almost half the power from standard operation caused the frequency to drop by 23% at the fast and furious end, which has a knock-on effect on performance. As was perhaps to be expected, for our throughput benchmarks, it was sizeable. For this data, we’re going to represent the performance uplift from 95W to the ‘unlimited power’ mode:
The system and office tests, which are a mix of latency and throughput tests, saw just under a 10% gain going from 95W to unlimited mode. For pure throughput however, that 23-24% difference in frequency gave an equivalent gain to the unlimited power mode. The only flipside is power: the extra performance pushes power consumption to 164-165W, which is a 74% power gain. If we were going for performance per watt, then the 95W wins that battle very easily. It all depends if the form factor the processor is in can provide sufficient cooling.
Doing these numbers gave me an idea for a metric for power efficiency. We currently run our power tests during a run of POV-Ray, and as a result, we can plot the power consumption during our POV-Ray test against the POV-Ray result score.
The highest performers are at the low end of the spectrum of what we’ve tested, with the Ryzen 5 2400G and Core i5-8305G (Kaby Lake-G) being the top performers, getting an efficiency rating (score/power) of 67 and 53 respectively. However Intel’s Skylake-X parts and the Threadripper 2990WX all scored highly on this metric too, around the 43 mark. This is likely because these high-power processors actually give less power per core, and each core is nearer to its peak efficiency for frequency/voltage.
The Intel Core i9-9900K, in normal operation, scores an efficiency rating of 32.9. This rises to 44.2 if the processor is fixed to 95W. This ultimately puts the 9900K in the limelight for an SFF system: when the power is limited to 95W, you get all the single core performance, most of the variable threaded performance, and around a 10-27% loss in throughput testing, most noticably in rendering. Overall, it acts like a 9900K in single thread mode, and like a 9700K in multi-thread mode.
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duploxxx - Thursday, November 29, 2018 - link
Interesting in a way that there are so many people that always believe in benchmarking and that in real world all cores are always idle....The world of wonders. Artificial TDP, turbo modes and decreased frequency when running multiple cores. All to fool consumers and benchmark believers.
Very nice review. Now the question:
can this also be tested on a Ryzen 2700 and a 8700K and a 9900. Put all 3 albeit in a different setup on a stock or even reduced cooling device and see how they behave....
olde94 - Thursday, November 29, 2018 - link
I see why you are intested, but both 2700 and 8700k are actually quite close in power use to their rated TDP. The issue was that the 9900k wasn't at all. If you see the power/performance graph on the last page, i think you have your answer ;)notashill - Thursday, November 29, 2018 - link
It's almost a very nice graph but could really stand to have a few more CPUs labeled. I mean even the literal headlining CPU that the entire article is about isn't labeled.And trying to compare to the POV-Ray results earlier in the article either a bunch of the CPUs are missing or the scale on the chart does not actually match the labels.
duploxxx - Thursday, November 29, 2018 - link
according anandtech measurements:2700x 105w rated buring 117.18
8700k 95w rated buring 145.71
9900k 95w rated burning 168.45
so no i ma not kidding. even the 8700k will have reduced performance with real tdp limit vs glorious benchmarking with best of best mobo and cooling.
4800z - Thursday, November 29, 2018 - link
No the 9900k and 8700k would have no lower performance on games. This only comes up when maxing out all cores for things like cinibench.TheinsanegamerN - Thursday, November 29, 2018 - link
Unless a game pushed those TDPs up. Games that can use many cores at once, like CIV and battlefield. You know, two minor franchises nobody would notice.....rhysiam - Friday, November 30, 2018 - link
There's a big difference between starting to use 6-8 cores (like Civ & BF) and hitting all those cores with a heavy load for a sustained period. Show me a game benchmark that has the 9900K literally doubling the performance of a 7700K and then you'll have a game that can push the 9900K well past its 95W tdp.Game streaming from a single PC would certainly do that, but I'd hopefully streamers are doing some research and choosing hardware carefully.
To be clear, I'm not defending Intel here, the tdp figure has become a joke, but we're a long way from this being a widespread issue for gaming workloads.
mr_fokyou - Thursday, November 29, 2018 - link
not if you are streaming while gaming than you are very much bottlenecking 9900k if u force TDP limitsbananaforscale - Saturday, December 1, 2018 - link
You are assuming no game uses all the cores (or enough that they go above TDP). The assumption is incorrect now and it will become more incorrect as quad core becomes the minimum.Samus - Saturday, December 1, 2018 - link
I think it's totally insane a CPU can use 25-27% more power than its advertised rating. Sure, that includes more performance, but as a system builder this has got to be a liability if you are putting together, say, a little 1U rack for video encoding security camera feeds. You would use a specified CPU based on its performance AND advertised TDP rating, only to find out to GET that performance, it needs to go well beyond its TDP rating, which likely wont be possible in a tiny rack with a 1U cooler (I don't believe they make 1U coolers rated beyond 105W - and those are incredibly rare, most are 73w-88w)