sched: Export ns irqtimes through /proc/stat

sched: Export ns irqtimes through /proc/stat

CONFIG_IRQ_TIME_ACCOUNTING adds ns granularity irq time on each CPU.
This info is already used in scheduler to do proper task chargeback
(earlier patches). This patch retro-fits this ns granularity
hardirq and softirq information to /proc/stat irq and softirq fields.

The update is still done on timer tick, where we look at accumulated
ns hardirq/softirq time and account the tick to user/system/irq/hardirq/guest
accordingly.

No new interface added.

Earlier versions looked at adding this as new fields in some /proc
files. This one seems to be the best in terms of impact to existing
apps, even though it has somewhat more kernel code than earlier versions.

Tested-by: Shaun Ruffell <[email protected]>
Signed-off-by: Venkatesh Pallipadi <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
LKML-Reference: <1292980144[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>