Using Voltage and Frequency Adjustments toManage Dynamic Power - Computer Architecture Techniques for Power-Efficiency - page 44

FIGURE 3.11: Razor voltage control system. The error rate is measured ( E sample ), compared to a
reference error rate ( E ref ) and a voltage level is selected to minimize their difference. Reproduced from
[ 73 ]. Copyright 2003 IEEE.
Timing errors, and the more rare meta-stability errors, have a negative impact on perfor-
mance. Absence of errors, on the other hand, could mean that voltage is not scaled aggressively
enough for the frequency. The Razor voltage control system is based on monitoring the error
rate and works to maintain a constant error rate, E ref If the measured error rate E sample is less
than the reference rate, then the voltage is further scaled downwards. In the opposite case, the
voltage is increased to reduce the error rate.
Razor has been tested in real chips (modified ARM cores) and has been shown to work
well. Substantial power savings (64% reported in their first paper [ 73 ]) can be expected by
breaching the voltage margins in the designs. But lowering the voltage for any significant
gain is also bound to cause a significant number of timing errors which will then affect both
performance and energy. Performance overhead from timing misspeculations is at about 3% in
their first study.