sched: Intoduce get_cpu_iowait_time_us()

sched: Intoduce get_cpu_iowait_time_us()

For the ondemand cpufreq governor, it is desired that the iowait
time is microaccounted in a similar way as idle time is.

This patch introduces the infrastructure to account and expose
this information via the get_cpu_iowait_time_us() function.

[[email protected]: fix CONFIG_NO_HZ=n build]
Signed-off-by: Arjan van de Ven <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: [email protected]
LKML-Reference: <20100509082523.284feab6@infradead.org>
Signed-off-by: Ingo Molnar <[email protected]>