IBM: Power chips get improved power management

At the Hot Chips meeting, IBM revealed that it plans to add a new sleep mode to its Power7 processors. During deep sleep, which Big Blue dubbed Winkle, the CPU draws virtually no power.

The new sleep mode, named after Rip van Winkle, extends the powersave capabilities of IBM’s Power7 chips. The three existing sleep modes, ‘nap’, ‘sleep’ and ‘heavy sleep’, are thus given an extra variant that makes an even deeper sleep possible. The heavy sleep mode reduces the power consumption of the eight cores by 85 percent and the cores become active again within two milliseconds.

Winkle reduces power consumption to near zero, but the downside of that frugal state is the time it takes to reactivate the cores; that lasts according to IBM engineer Michael Floyd ten to twenty milliseconds. It is not yet known whether the current Power7 processors will get the new sleep mode on board with an update. Given the statement that the technology is ‘a little teaser for future chips’, IBM could wait until the Power8 introduction.

In addition to Winkle sleep mode introduced Floyd new features of the EnergyScale power management in the Power7 chips. By reducing the so-called guard bands, or safety margins, the processors can become more effective. The guard bands ensure that the signals are not disturbed, but the margins of the measures could be stricter. In EnergyScale, a critical path monitor adjusts margins in real time to keep them as low as possible. That would allow an overclock of more than seven percent or an energy reduction of almost 16 percent.

Power7-EnergyScale also received a low-energy-detection technology that clocks down cores with a low workload. Per millisecond, the clock rate can be reduced by 50MHz, in steps of 25MHz. The third energy-saving measure in the new EnergyScale is a way to indirectly measure the energy consumption of a core; IBM calls it Power Proxy. This allows the power of the processors to be regulated on the basis of indirect measurement data. That should lower the power consumption based on activity of the individual cores, despite the lack of voltage regulators on the individual cores in the IBM processors.