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This is the third post documenting my upgrade to an Intel Core i7 Lynnfield system. In my first post I discussed the components I selected and why. I talked about assembling the system and some of the challenges I encountered in my second post, and in this final post I’ll be discussing my efforts at overclocking the Intel DP55KG motherboard and Core i7 860 processor.

Two Approaches

Intel’s new “Turbo Mode” feature is able to increase the processor multiplier value beyond its default value (21 in the case of the Core i7 860) if the processor is operating within what it considers are safe temperature parameters. For example, in Intel’s Core i7 Bloomfield architecture, processors are allowed to raise the stock multiplier value by 1 or 2 depending on the number of cores being used. Intel’s Lynnfield processors are considerably more aggressive with Turbo Mode, increasing Turbo Mode multipliers within a range of ~2-5. Essentially what this means is that when fewer processor cores are demanded by an application or process, larger multiplier values are used, thus the processor is allowed to run faster than the default multiplier would normally allow. In the case of the Core i7 860, it’s not uncommon, for example, to see it use a multiplier value of 26 in single-threaded applications, yielding a processor speed of 3.46 GHz, well above its stock speed of 2.8 GHz. While this sort of dynamic overclocking is pretty damn impressive, a question arose for me when it came time to overclock my Intel DP55KG and Core i7 860: should I attempt to overclock the system with Turbo Mode enabled, meaning I would have to consider the headroom required when higher multiplier values are used, or should I simply disable it and go with the more traditional overclocking approach? I ended up trying both approaches to see how they compared and to evaluate which would work best for me.

Regardless of which approach you use though, overclocking a Lynnfield system is pretty straight forward. Adjust the host clock frequency until the system achieves a stable CPU speed. From there, the memory multiplier can be adjusted to compensate for the change in host frequency. If desired/needed you can also adjust the CPU voltage, memory voltage, and Uncore voltage to further stabilize the system. That’s pretty much all the adjusting the architecture allows you to do.

Turbo Mode enabled

My first attempt at overlocking the Intel DP55KG and the Core i7 860 involved raising the host clock frequency but leaving with Turbo Mode enabled. These are the BIOS settings I started with:

Performance

Host Clock Frequency Override: Manual

Performance -> Processor Overrides

CPU Voltage Override Type: Dynamic
CPU Voltage Override: Default (default)
CPU Idle State: High Performance
Intel Turbo Boost Technology: Enabled (default)

Performance -> Memory Configuration

Performance Memory Profiles: Manual – User Defined
Memory Multiplier: 12
Memory Voltage: 1.65
Uncore Voltage Override: 1.10 (default)

Performance -> Bus Overrides

All settings in this section were left at their default values.

Power

Enhanced Intel SpeedStep Tech: Enabled (default)
CPU C State: Enabled (default)

With this approach, my objective was to try to achieve the best stable overclock I could using Turbo Boost and leaving the voltage settings at thier default values. However, I did alter two voltage settings: the CPU Voltage Override Type, which I set to Dynamic, allowing the CPU to still manage its own power usuage but with higher upper limits; and the Memory Voltage, which I set to 1.65 to match the voltage input specified for my Mushkin DDR3-1600 kits. I left the RAM timings at the default SPD values of 9 9 9 24.

And the result? I was able to achieve a host clock frequency of 154 MHz before the system became unstable (stability in this case is defined as the ability for the system to run without failure using Prime95 (v25.9) Large FFT for 2-3 hours). This yielded a CPU speed of 4 GHz, assuming a Turbo Boost multiplier of 26 (154 * 26 = 4.00 GHz). I did notice, however, that the multiplier in my case generally liked to stay at 25 a large percentage of the time during idle. I suspect this was the result of the High Performance setting in BIOS that forces the system to use the higher multiplier when the operating system would otherwise be allowed to lower it.

According to CPU-Z (v1.53) The CPU voltage (VID) fluxuates between .8 and .9 at idle and core temperatures according to Speedfan (v4.40) were ~30c at idle. Given the DRAM multiplier setting of 12, the DRAM frequency weighed in at a nice 1848 MHz. Loading all four cores resulted in VID rising to 1.096 volts and core temperatures to ~63c. Using all four cores of course also resulted in the system using the default CPU multiplier value of 21 (154 * 21 = 3.23 GHz).

So, in summary, I was able to achieve ~15% overclock under load using Turbo Boost and leaving the voltage settings at thier default values.

Turbo mode disabled

After determining the optimal overlocking settings for my Intel DP55KG and the Core i7 860 using default voltages and Turbo Mode enabled, I attempted to overclock the system with Turbo Burst disabled as well as the freedom to use higher voltage settings, if necessary, to make the system stable. These are the BIOS settings I started with:

Performance

Failsafe Watchdog: Enable (default)
Host Clock Frequency Override: Manual
Host Clock Frequency: 133

Performance -> Processor Overrides

CPU Voltage Override Type: Static
CPU Voltage Override: Default (default)
CPU Idle State: High Performance
Intel Turbo Boost Technology: Disabled

Performance -> Memory Configuration

Performance Memory Profiles: Manual – User Defined
Memory Multiplier: 10
Memory Voltage: 1.65
Uncore Voltage Override: 1.10 (default)

Performance -> Bus Overrides

All settings in this section were left at their default values.

Power

Enhanced Intel SpeedStep Tech: Disabled
CPU C State: Disabled

And the result? With Turbo Burst disabled and the latitude to increase VID and other voltage settings if necessary, I was able to achieve a host clock frequency of 170 MHz using a VID of 1.2 before the system became unstable, yielding a CPU speed of 3.5 GHz (170 * 21 = 3.57 GHz). Further increases in VID, memory or Uncore voltage did not allow for a stable system using higher clock speeds. Core temperatures rose to ~35c at idle and loading all four cores caused the core temperatures to rise to ~74c. With a the DRAM multiplier setting of 10 instead of 12, the DRAM frequency fell to 1700 MHz. Here again I left the RAM timings at the default SPD values of 9 9 9 24. I did try to run with the DRAM multiplier set at 12 but there was just no way my 1600 MHz RAM was going to run at 2040 MHz!

So, in summary, I was able to achieve ~28% overclock under by shutting down Turbo Boost and raising VID to 1.2.

Comparison

Table 1 shows the results of few highly unscientific tests I threw at both cases to see how they compared.

Table 1

	h.264 Encoding (Minutes)	SiSoft Sandra Memory Bandwidth (GB/s)	SiSoft Sandra CPU Arithmetic (GOP/s)	3DMark Vantage (1280x1024, 4xAA)	X3 Terran Conflict (1280x1024, 4xAA)	BattleForge (1280x1024, 4xAA)	Crysis (1280x1024, 4xAA)
Stock	33	17	71	15904 (15311/17996)	92	77	45
Turbo Mode On	25	22	80	16732 (15750/20587)	109	77	46
Turbo Mode Off	23	18	87	15342 (14209/20160)	118	81	47

The h.264 tests involved transcoding a typical MPEG-2 DVD *iso to the h.264 high-profile format using Handbrake. You can see there was not a significant difference in time between the two methods, but both represented a nice improvement over the default settings. Turbo Boost, however, did provide a nice bump in memory bandwidth, due mostly to the ability to run at a higher DRAM multiplier value. The use of Turbo Boost also wins out where 3DMark Vantage is concerned, suggesting that the higher multipler values played a role here again (the results show the overall scores followed by the GPU/CPU score in parenthesis). The game-based tests were vitually useless since these particular games strongly rely on the GPU and not the CPU. However, a game like X3 Terran Conflict, which likely makes use of all four cores for physics calculations, clearly benefits from the higher host clock speed.

Conclusion

Turbo Mode is something that should be evaluated based on your needs and the specifics of your overclock. Which one did I go with? I decided to run with Turbo Mode enabled and the lower host clock frequency. There were a couple of reasons for this choice. First, I rather like using the default voltage settings; by allowing Intel to manage the power settings, I’m able to run my system moderately faster, and in some cases a hell of a lot faster, but also a lot cooler. Second, I typically run applications that do not utilize all four cores, so a moderate overclock with Turbo Mode gives me better results than a higher-speed overclock without Turbo Mode. However, it’s good to know that as I grow to depend on more cores consistently, I can simply shutdown Turbo Boost and clock the system higher.

Related Posts

• My Intel Core i7 Build: The Parts
• My Intel Core i7 Build: Putting It Together

Tags: Hardware, Windows