Overclocking iA Processors at IDF2013
September 10, 2013, Intel Developer Forum, San Francisco—Michael Moen and Dan Ragland described the capabilities and techniques for overclocking an iA processor for better performance in gaming and content creation. Although they disclaim any responsibility for damage, they illustrate all the knobs and buttons.
Overclocking increases performance by increasing clock and system frequencies. This process also requires increasing the voltage on the processor, memories, and the interfaces calling for vastly increased cooling capabilities for all system components. Increasing the power limits and current for the core processor(s) and increasing core ratios helps in compute intensive functions like render, transcode, gaming physics, and AI.
For media transcode and faster game frame rates in the APUs, you must also raise the pGfx voltage and the pGfx max ratio. Memories are speeded up by increasing memory ratio, raising memory I/O voltage, speeding up timing, and increasing system agent voltage for photo and video editing. By combining all of the changes, the perform base clock provides al of the performance enhancements, but care is required to reduce the weakest domain frequency via ratios.
Records for the modifications for high-end desktop machines including socket LGA2011 parts are around 6 GHz for core i7 965x, 7 GHz for core i7 980x, 5.5 GHz for 3960x and 6 GHz for 4960x chips. For the mainstream core i7 processors, a 875K gets to 5.2 GHz, 2600K achieves 6 GHz, 3770K over 7 GHz and the 4770K gets to 6.8 GHz. Not all systems can achieve these values and are for illustrative purposes.
For socket LGA2011 chips and X79 chipset, the core frequency is determined by the core ratio, which has 63 increments in 100MHz increments. Memory ratio is granular in 266 MHz steps through DMICLK (aka BCLK) and has fine grain adjustments of +/- 7 percent. PEG and DMI ratios are 80/50. 64/40, and 48/30 and must reflect the BCLK coarse ratio. For example, a core frequency x 1.25 requires PEG/DM ratio of 64/40 x 1.25 to keep at 8GHz / 5GHz nominal.
To sustain the higher performance, PCBs and power supplies need to be designed for high dynamic range and capacity with suitable headroom. The traces need to be designed for the power and for good signal integrity, with short lengths, length matching, and more layers in the board. Very high grade active and passive components are essential. In addition, the bios and additional hardware have to be overclocking compatible and the UEFI should have extensive auto-rules for all parameters.
The Haswell processors with integrated graphics have some different characteristics. The core ratios are up to 80 in 100MHz increments and voltages are programmable via iVR. The graphics ratios are up to 60 in 50MHz increments, memory ratio is in either 200 or 266MHz steps with logical ratios up to 2933MHz.
The Haswell processors also have integrated voltage regulators. The Vcore, Vring, and Vgraphics voltages are dynamically changed based on workload, and static voltage can be up to 2.0V. The system agent and I/O blocks can have up to 500mV offset from nominal. The input voltage can be up to 3.04V from a nominal maximum of 2.3V. the various operating modes are managed by the iVR. The BCLK allows PEG/DMI ratios of 5:5, 5:4, and 5:3, depending upon PCH frequency.
These modifications are applicable to all i7 and on i5 –H, -M, and –U series processors. The extreme memory profile (XMP) are loadable from bios or OS system-level tuning apps. A number of vendors make XMP compliant DIMMs and can be certified or uncertified for XMP operation. Check www.intel.com/consumer/game/extreme-memory.htm for details. An extreme tuning utility (XTU) is available for Windows users to manage the knobs for performance tuning without rebooting.
