Thursday, August 6, 2015

Intel's Skylake or: How to Boil Frogs Alive

Writing about ephemera is kind of depressing. It's the permanent things, or at least, the big changes, that produce a sense of meaning. A hundred years from now, people will still be picking up Marcus Aurelius' Meditations or St. Augustine's Confessions in search of meaning. Hard to imagine anyone reading through a Linux digest flamewar of what options for the graphics driver for the Nvidia GeForce GT230 will produce the best frame rates for Starfox or whatever it is Linux gamers play.

Sometimes you just have to write something down even if it is never again given life by another reader because it could be. A thought written down can never be truly forgotten. Stick with your wife.

Intel's Skylake is officially out. It's largely the same story it has been since Sandy Bridge Bloomfield. Single digit IPC improvement over Broadwell which has single digit IPC improvement over Haswell which has single digit IPC improvement over Ivy Bridge which has single digit IPC improvement over Sandy Bridge which has single digit IPC improvement over Clarkdale which has single digit IPC improvement over Wolfdale which has single digit IPC improvement over Conroe which has significant double digit IPC improvement over Prescott. 

This is why every single Intel CPU review published since Sandy Bridge has a comment along the lines of "Disappointing. I guess I'll be sticking with my overclocked i5-2500k". If you read the artlessly struck out text, you might be wondering why Sandy Bridge is the hero when Conroe saw the largest generational leap in performance. The prior Core series was legendary, in particular the Q6600. But 2500k could overclock to 4.5GHz easily whereas the Q6600 topped out around 3.5GHz. A 30% clockspeed advantage multiplied by several generations of small IPC improvements, a gaming environment with less extreme GPU bottlenecking, and a bargain basement price created the legend.

Imagining a similar jump, I can guarantee you that an i5/i7 that could easily overclock to 5.8GHz today would put to rest any complaints about the languid pace of CPU improvements.

Instead, we have yet another quadcore 4.x GHz i5/i7.

The IPC gains, even with the optimistic assumption that users spend a good chunk of their time rendering 3D cinematics and transcoding video, are about 25% from Sandy Bridge to Skylake. Most people buying high performance computers these days are gamers, and in most games they will realize single digit gains if any. This isn't Intel's fault since games are mostly limited by graphics cards these. Intel did its part and CPU performance hasn't been a bottleneck for years. Even in unique cases like ArmA which are CPU bound, the increase is probably 15% tops since a large portion of the improvements have been in circuitry designed for specialized workloads, i.e., AVX which ArmA and most games do not use.

My own test with a Sandy Bridge i7 overclocked to 4.6GHz in DayZ running around Cherno is a minimum FPS of about 25. Switching to Skylake will require a new motherboard and RAM in addition to a new CPU/cooler. It's really not that expensive to upgrade, even if I were to upgrade to Skylake E from my current Sandy Bridge E system, but all that money and effort for an increase of 4 frames per second?

On the other hand, early indications, just like the early indications were for Ivy and Haswell are that Skylake will be a good overclocker. Non Ivy-E and Haswell-E were plagued by Intel cheaping out on thermal interface material and a focus on power savings which led to rather poor overclocks and essentially no improvement over a comparably overclocked Sandy Bridge system. It is only with Ivy Bridge E, Haswell E, and Devil's Canyon processors that one could experience actual performance gains in OCed systems.

While the high TDPs for Skylake suggest a renewed focus on desktop performance, it might be the case that even with a very good watercooling setup, the chip just won't overclock that high. On the graphics card side of things, moving to watercooling from aftermarket air has not helped clocks for AMD's Fiji or Fury. Nvidia's Titan X/980Ti gains mere single digit percentage improvements.

The thermal limitation might be there, but a significant realized improvement will likely be relegated to sub-zero cooling. Perhaps cascading heat pipes* to a water loop could manage it in an ATX form factor, but even if such a wonder cooler were developed, other chips could also benefit bringing us back to looking at IPC.

In the end, I think these tiny IPC improvements with OCs in the mid to high 4GHz range are all that's left in the cards and years from now when the i5-9500k is reviewed, someone will bring up the 2500k. By that time it will have become something of a joke; the "can it run Crysis?" of its time, though, barring a quantum leap in GPU performance, it will ring true. DX12 and VR only exacerbate the current GPU bottleneck which leaves Intel with very little incentive to abandon its mobile/power saving/marginal improvement roadmap.

These minutiae, these infinitesimal increments to improve something in a vanishingly small arena, however, is how we got to where we are today. For all the geopolitics and academic fighting between Capitalism and Communism, the difference between them from a per-capita GDP perspective is about 3.61%.

Put that way, the entire Cold War and socialist upheavals seem misplaced, but over the course of a lifetime, it matters. If you took two kids who grew up in the ruins of Germany after the Second World War, one in West Germany and the other in East Germany (with its cooler anthem), the one in the West might be contemplating whether he should get a BMW, Mercedes, Audi, or VW, which models he would like, and inspect dozens of cars at several dealerships to decide.

The one in the East would probably still be on a waitlist for a car made of plastic and cotton.

* Just to be clear, I mean cooling the heat pipes with water not using multiple heat pipes to somehow defy the laws of thermodynamics.

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