[RFC][patch 0/1] nohz delay performance optimization

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

Greetings,
I'm still working on the cpu idle/wakeup path to improve the performance
of some ping-pong workloads. This patch is the latest idea and proved
rather effective. The idea is that the timer tick is not switched off
if the cpu did some work in the last tick period. This will add an
unnecessary tick interrupt if the cpu goes truly idle but will save
some cycles for the nohz reprogramming if the cpu wakes up again for
more work.

Currently the patch only works on s390, the arch_needs_cpu() will be
true if there has been any other interrupt than timer interrupts in the
last tick period. I think this could be improved with an explicit
call to request a nohz delay. The call should be added to selective
points in the code, e.g. whenever a process != idle is scheduled,
whenever a bottom half is run, and so on.

Comments?

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.