The Haswell Review - Intel Core i7-4770K Performance and Architecture
Integrated Voltage Regulator and Overclocking Haswell
Haswell's New IVR
One of the more interesting design changes to Haswell that isn't really a part of the architecture itself is the move to an integrated voltage regulator.
Unlike all previous processors from Intel and AMD, Haswell actually moves the job of legacy power delivery from the PCB of the motherboard directly onto the die of the processor in silicon. This has the advantage of simplifying platform design because now vendors only need to provide a single, clean input voltage to the processor and it handles the rest of the work.
Power to the memory is still handled by the motherboard but otherwise the delivery of voltage to the cores, the processor graphics, the ring bus, IO and the system agent is all handled by a digital power system on Haswell. Intel claims this allows them better flexibility when it comes to designing lower power processors and platforms that find their way into tablets and also can provide more granular power delivery for better power management and sleep states.
For motherboard engineers though, this was kind of a bummer - one of the key differentiation points for motherboard design was in power delivery, phase technology and topology. By moving so much of that into the processor and on silicon Intel is effectively taking away one of the few remaining areas for motherboards competitors to...compete on. Remember when memory controllers and performance would vary motherboard to motherboard? Another one bites the dust.
Overclocking with Haswell
Overclocking with Haswell is very similar to overclocking with Ivy Bridge with the addition of a new control point for base clock ratios.
If you remember when Sandy Bridge-E launched, Intel had figured out a way to allow base clock ratio increases to steppings of 125 MHz, 166 MHz and 250 MHz; though the 250 MHz option is obviously a pipe dream. With Haswell that same option makes it way to mainstream consumer processors, at least for the K-series parts that is. One contentious point during our briefings with Intel was why they would lock that ratio on the other processors now that the problem has been solved. (Keep in mind that Intel claimed they couldn't TECHNICALLY enable base clock ratios on SNB or IVB without stability issues.)
Otherwise though, overclocking Haswell is the same as Ivy Bridge and Sandy Bridge though with some additional care to the voltages. Things have changed as you are now controlling an input voltage (the one we actually going from the motherboard to the processor) and then voltages on the integrated voltage regulator. Base clock, ratios - it's all there.
Looking at the new UEFI on the Intel Z87 motherboard (which is actually really nice!), we see a handful of new settings. The first voltage option we'll consider is the core voltage that allow us to reach higher clocks either through a fixed multiplier or Turbo ratios. There are three different options for that voltage, which is likely the most important setting, so Intel provided these three diagrams to demonstrate.
The offset mode applies a positive or negative offset to the voltage over the entire voltage curve that is natively built into the Haswell CPU. This means voltages will be higher at idle, higher during Turbo and higher during the non-Turbo clock states.
An interpolated mode allows the voltage to scale only after it gets past the standard, default Turbo voltages.
Finally, the static and offset mode sets the voltage a fixed level through the entire performance curve. This is helpful if you are underclocking as well as overclocking with the base clock.
The second main voltage to adjust is the input voltage, the one coming in to the IVR. The default of this ranges from 1.7v to 1.8v depending on the SKU. Because the input voltage is related to the maximum voltage that the IVR can output to the cores, graphics, ring bus, etc, you may have to bump this up as you increase the other voltage rails.
This is where you can adjust the base clock ratio for higher base clock settings while keeping the PCIe and DMI frequencies in their safe zones.
5:5 (default) (i.e. BCLK 100: PCIe 100)
4:5 (BCLK 125:PCIe100)
Each motherboard will have different settings but it was recommended to us to disable features like Processor VR Faults and Processor VR Efficiency to get a more stable overclock at higher settings.
Adjusting the multiplier for the cores is simple enough and you should be in the normal range of the low to mid 40s. Intel recommends keeping the ring bus multiplier level at one lower than the cores.
Our Early Overclocking Results
I should be upfront here and just let everyone know the truth: Haswell doesn't overclock as well as SNB or IVB and it gets significantly hotter. In any event, we needed to see for ourselves how high we could push the part we had.
The best speed I could hit was 4.6 GHz on all cores with these settings:
- 100 MHz base clock
- 46x Core multiplier
- 45x Ring multiplier
- +100 mV ring voltage
- +200 mV core voltage
Based on my talks with other reviewers and hardware vendors, this is pretty typical and only very few processors are hitting the 4.8 GHz mark.
In our performance graphs on the following pages we'll show you a consistent Haswell running at stock speeds as well as the same chip running at 4.5 GHz - obviously performance is going to be better. But how does overclocking affect temperature and power consumption?
I should note that for our testing we used the Corsair H100i, a 240mm self-contained water cooler that is among the best on the market.
Temps at stock settings
Temps at 4.1 GHz
Temps at 4.3 GHz
Temps at 4.5 GHz
Temps at 4.6 GHz
There is a steady progression of temperature as we increase the clock speed and the jump from 4.5 GHz to 4.6 GHz was...bad. Seeing temperatures hover in the 90+C range is dangerous and caused the fans on the H100i to get quite loud too.
WOW. Load power consumption jumps from 127 watts on the Core i7-4770K at default settings up to 201 watts when overclocked to 4.5 GHz - that is an increase of 75 watts. For comparison, that is higher than the Core i7-3970X that uses 6 cores that are more power hungry and nearly hits the same power consumption levels of the AMD FX-8350. (Actually, that's just as bad for AMD's FX-series).
Enthusiasts lamented the fact that overclocking got easier but didn't scale better when Intel moved from Sandy Bridge to Ivy Bridge, and the same thing has occurred again with Haswell. Clearly Intel's focus on lower power designs has limited higher clock rates and expanded leakage on the high end. These are the cards we are dealt.