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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Rukur - Monday, December 3, 2018 - link
9900K comes out of the box with 5Ghz so its going to win on games. The prize it a game stopper but.woggs - Thursday, November 29, 2018 - link
"This rises to 44.2 if the processor is fixed to 95W" but there is no data point on the plot at that spot. A mouse-over labeling of that plot would be very-helpful.romrunning - Thursday, November 29, 2018 - link
I don't understand - the article title says "Fixing the Power for SFF", and yet no motherboards with the form factor typically used in SFF systems were actually tested. The motherboards listed were all ATX; no mini-ITX or even micro-STX boards were used.Why not? Wouldn't this have provided valuable insight for those looking to purchase a SFF system, custom or DIY, to see which mfgs cap the TDP usage or let it go full range?
The author said he tested a MSI Vortex G3 small form factor desktop last year. Well, why not get some comments from ASRock, Gigabyte, ASUS, and MSI as to whether it's standard practice for them to limit CPUs to a specific power limit in their BIOS for those SFF boards.
Fro example, I'd love to know if that sweet-looking ASRock DeskMini GTX Z390 that was recently reviewed can take the i9-9900k rated at 95W to the full "unlimited" power settings. I can put 450-600W SFX/SFX-L PSUs into a SFF system, so I'd like to know if I can get the full performance out of the CPU or if the mfg locks the power draw in the BIOS.
SaturnusDK - Thursday, November 29, 2018 - link
Why is this article, and Anandtech in general, using 1000 unit OEM prices for Intel products which are typically 15-20% less than the lowest retail price you can find. But use the highest you can find retail prices for AMD products? It seems like Anandtech is deliberate trying to make people think Intel products have any value when the reality is that they don't.Rezurecta - Thursday, November 29, 2018 - link
Good re-review. Although, Ian doesn't seem to want to call Intel out. This is OBVIOUSLY something initiated by Intel. If the 9900k were to run in spec it would be slower than the 2700x in a LOT of benchmarks. Intel couldn't have that for such a massive hot monolithic die. That's why all the shady sponsored benchmarks and having the processor way out of spec.It's obvious Intel is hurting. Let's hope this brings about a competitive landscape again.
kernel-panic - Thursday, November 29, 2018 - link
it would be nice if somewhere you let readers know what TDP, PL1 and PL2 mean. I enjoy this kind of articles but I'm not related with the terminology.Icehawk - Thursday, November 29, 2018 - link
It's in the (by now) linked article at the very beginningMr Perfect - Thursday, November 29, 2018 - link
How do motherboards treat the non-k versions of these CPUs? When I built my mITX machine, I bought the non-K processor since there wouldn't be any overclocking going on. Just how locked is a locked CPU? Technically, this could be considered turboing ratehr then overclocking and could be applied to the non-Ks.Targon - Sunday, December 2, 2018 - link
It is possible that Intel won't release a non-k version of these chips, just because there won't be a significant enough performance benefit vs. the AMD 2700X if the chips were not being pushed to their absolute limit.stux - Thursday, November 29, 2018 - link
An interesting point that you make is that a 9900K constrained to 95W performs like an unconstrained 9900K for single threaded loads and an unconstrained 9700K for multithreaded loads.The 9700K has half the threads, so that is an interesting claim, and I think the key is how does the 9700K perform when constrained to 95W.
Hyperthreading is supposed to be a big win to perf/W, thus I’d expect 9900K at 95W to be more efficient than the 9700K for the same perf, which is a definitive win too.
How does the 9700K at 95W perform in the multi threaded benchmarks?