Intel's Game Changer: One Size Fits All Haswell
Integration with Windows 8
The next slide shows Windows 7's default activity, its activity when scheduled tasks are aligned with processor active cycles, and Windows 8's default scheduling.
In the Windows 7 comparisons, the black tick marks are 15.6ms apart. There are 7 ticks, for a total of 109.2 milliseconds, or roughly a tenth of a second. With default scheduling, the CPU only idles a full 15.6ms twice. From the first tick to the second, the chip drops into idle ~40.2% of the time. Aligning poll timers and grouping deferrable requests together under Windows 7 significantly improves the situation; the CPU spends 87% of its 15.6ms window in idle mode between ticks 1&2.
Windows 8 jettisons the system timer altogether, discourages poll timing, and aligns activity more stringently. As a result, the system spends a much higher amount of time in idle or low-power mode, even dropping into a CPU power-off state at one point. Because we're still talking about milliseconds, the end user hasn't even noticed the difference -- but the device's battery will.