Devil’s Canyon Lessons
The idea came up to revisit Devil’s Canyon using retail samples. It seemed like most of last June’s Core i7-4790K coverage saw reviewers landing around 4.7 or 4.8GHz with four cores under load. Might refinements made over the last year change that? And what about the impact of boxed parts rather than our pre-production CPU?
Haswell-E is going to endure beyond the launch of Skylake, though. It made more sense to do an overclocking test using Core i7-5960X instead. Plus, the -5820K, -5930K and -5960X all use solder as an interface material instead of a polymer. It dawned on me that we never really asked Intel ahead of the Haswell-E launch whether those parts benefited from the lab work gleaned from Devil’s Canyon. I followed up after our initial chat with a series of email questions, which Paul answered in more depth than we often get from Intel:
Tom’s Hardware: Did Intel use any of the experience that went into Devil’s Canyon to improve overclocking on Haswell-E?
Paul Zagacki: Yes. In fact, we used many of the learnings from the Devil’s Canyon analysis and optimization to improve the overclocking experience of HSW-E. With double the core count, -5960X’s total consumption under extreme overclocking can be very high. To ensure those four extra cores scaled well, we allowed additional power delivery by uncapping Icc Max. We also added a knob to allow enthusiasts to increase the thermal throttling point (we didn’t want a few degrees to get in the way of that last bin). This is something we explored for Devil’s Canyon, but found the throttling knobs weren’t limiting, so they were never released into the wild.
Tom’s Hardware: Was the impact any different on the larger HSW-E die compared to quad-core Haswell?
Paul Zagacki: In general, a larger die area benefits single-threaded thermals with more area under the IHS to spread the power. But all cores overclocked becomes more dependent on overall effectiveness of the thermal solution to bring the extra power out of the package. All of those cores running can quickly become power delivery-limited. Power = CV^2F (more or less) and is a cruel mistress, especially when it takes any extra voltage to get the frequency. Adding cores linearly scales the switching capacitance for any given workload.
Tom’s Hardware: What other knobs don’t get enough attention when you see enthusiasts trying to maximize an overclock or dial in stability?
Paul Zagacki: As you know, the extreme overclockers leave no stone unturned. But casual overclockers don’t seem to play with the real-time knobs accessible via Windows. Many of Intel’s overclocking settings can be changed live within the OS. Overclockers can improve their reliability by dynamically changing frequency, voltage, power limits, etc. Intel’s Extreme Tuning Utility, for example, offers a streamlined interface for making such adjustments. It’s a handy tool for overclocking and has some options to dynamically apply different profiles based on the applications running on your system. For example, XTU can dynamically overclock the processor when a specific game starts up. On top of that, we have put a lot of thought into how to recover a system when you’ve gone off the deep end with a set of overclocking knobs. There are a number of features within the CPU and chipset that sense when we are hung and can automatically reset the platform to a place where a simple recovery to a safe operating point is possible.
Tom’s Hardware: With all of this talk about Devil’s Canyon and Haswell-E, what are the top overclocks you’ve seen in Intel’s lab?
Paul Zagacki: On Core i7-4790K, we were seeing a strong population of parts reaching 4.9 and 5.0GHz for 4C/8T on water cooling. We have the ability to look at a lot more silicon than your average overclocker, and then can correlate those results back to data we see in manufacturing and test to project against huge populations of data. Our focus for Devil’s Canyon was on what a typical enthusiast would do in this space, generating stable results and focusing less on things like getting the best-case frequency snapshot, single-threaded or LN2.
Core i7-5960X overclocking has also been amazing. Even with eight cores, the top clock rate is only slightly lower than the four-core -4790K, with some units clocking in as high as 4.7-4.8GHz. This is pretty amazing considering all the additional power/temperature and resulting voltage drops you have to manage with 4x the switching capacitance from the additional cores. Also, we’ve also seen DDR4 overclocking above 4,000 MT/s. This is truly amazing—DDR4 was just released and the officially supported maximum frequency is 2133. With all those cores running, you have to feed them, so the DDR4 overclocking helps you realize a lot of performance you gain from tuning your cores.
