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Overclocking: Can Sandy Bridge-E Be Made More Efficient?

Overclocking: Procedure, Details, And Log

Let's get down to business. Our first question is whether we should be enabling Turbo Boost or not while we overclock manually. Although power management and automatic tuning mechanisms are great behind-the-scenes features for folks who don't like to mess around under the hood, they generally aren't idea for generating clear, scientific results.

Nevertheless, Turbo Boost turns out to be one of the best ways to fine-tune performance at any given load level. So long as you're able to manually specify clock rate based on however many cores are active, you can control how much voltage is required to maintain a stable system in any given workload.

Overclocking With Second-Gen Turbo Boost

And so, we made the decision to overclock with Turbo Boost enabled. In fact, per Intel's guidance to motherboard vendors, overclocking on platforms wielding unlocked processors is achieved through Turbo Boost ratios. We increased our maximum TDP and maximum current limits to create additional headroom, and went about increasing the multipliers.

We also enabled power-saving features wherever possible. In practice, you want to cut back on consumption as much as you can during idle periods, even as you push performance up under load.

The multiplier combinations we used are listed below. Turbo Boost is able to specify multiplier settings based on processor activity. Using a base clock of 100 MHz and a default multiplier of 33x, the following combinations are then allowed to modify that 3.3 GHz product.

Overclocking Table

Stock ConfigurationOverclock #1 (Mild)Overclock #2 (Mild)Overclock #3 (Moderate)
Five or Six Cores Active36x38x40x42x
Three or Four Cores Active37x39x41x43x
One or Two Cores Active37x41x43x45x
Idle Voltage (Measured in AIDA)0.846 V0.846 V0.846 V0.846 V
Load Voltage (Measured in AIDA)1.241 V1.286 V1.316 V1.336 V
Firmware Voltage SettingDynamicDynamicDynamicOffset 40 mV
Overclock #4 (Moderate)Overclock #5 (Moderate)Overclock #6 (Aggressive)Overclock #7 (Aggressive)Overclock #8 (Aggressive)
Five or Six Cores Active43x44x45x46x47x
Three or Four Cores Active44x45x46x47x47x
One or Two Cores Active45x46x47x47x47x
Idle Voltage (Measured in AIDA)0.846 V0.846 V0.846 V0.846 V0.846 V
Load Voltage (Measured in AIDA)1.321 V1.326 V1.331 V1.331 V1.336 V
Firmware Voltage SettingOffset 40 mV1.34 V1.355 V1.37 V1.385 V
Stable?YesYesYes Mild V-DroopYes Low V-Droop PLL Override: Enabled Idle State: High Performance

Voltage Overview

The following table shows which voltages were used for the other core components of the test system.

Processor Core (V)Dynamic
Memory (V)1.65 V
System Agent Voltage (V)1.05 V
Processor I/O (V)1.05 V
Processor PLL (V)1.8 V
PCH Core (V)1.1 V

Overclocking Log Book

Turbo Boost Multiplier Settings: 42-43-45 and 43-44-45

The platform froze at 4.5 GHz using dynamic power in single-core mode. After applying a 40 mV offset, the system stabilized. The same problem surfaced when we tried the next-highest multiplier ratio, though. We prioritized multi-core performance and reduced the third ratio setting from two bins to one. This allowed stable operation without further changes to the test configuration.

Turbo Multiple Settings 44-45-46

Changing the offset to 120 mV allowed the machine to boot; only a manual voltage adjustment helped. But this allowed us to reach the speed at which energy efficiency fell off sharply.

Turbo Multiple Settings 45-46-47

This case also didn't allow for simple voltage increases. We had to switch from High V-Droop to Mid V-Droop, which again led to increased power consumption. This is a good way to dial in more stable performance, but not to improve efficiency.

Turbo Multiple Settings 46-47-47 and 47-47-47

We weren't able to stably reach 4.8 GHz, although all the cores eventually reached the 4.7 GHz mark. For this step, we had to disable the rest of the energy-saving functions, which accounts for the really bad efficiency results, as we had to:

  • enable Low V-Droop
  • set PLL Override to High
  • set Processor Idle State to “High Performance“

After these adjustments, the test system consistently ran at 4.7 GHz. Interestingly, the single-threaded performance was influenced by raising the Turbo Boost setting for 3 + 4 cores, due to non-optimal scheduling in Windows.