TODO

Ensure irq work use self-IPIs and not hooks on the timer tick (per arch property, should be a Kconfig). ARM currently misses this, fix in the way: http://lkml.kernel.org/r/20131018163740.GA21983@codeaurora.org
Support rq->cpu_load. Its decaying supports well dynticks idle but doesn't work buzy dynticks. Some attempt to solve that, see http://lkml.kernel.org/r/1371761141-25386-1-git-send-email-fweisbec@gmail.com
Update rq->rt_avg decaying
Update rq->calc_load_active
Revisit the idle load balancing logic to make it working with adaptive tickless kernels.
Add some automated debugging checks that ensure we are not dealing with stale rq clock values due to missing update_rq_clock() calls. We have some accessors like rq_clock() and rq_clock_task() that we can fill up with stale timestamp check. We need to mark the scheduler entrypoints that may end up using the rq clock though. This is a broader concern that just full dynticks, of course the periodic tick lowers the impact of a stale clock.
We could shut down the tick even when more than one tasks are running using hrtick for preemption. But peterz said it's a bit broken and can be costly due to frequent writes on the hardware clock. That needs testing I think. This may be a win compared to keeping the periodic tick.