* Ingo Molnar <[email protected]> wrote:
> The TIF_RCU_QS thing is just a fancy way for synchronize_rcu()
> (being executed on some other CPU not doing RT work) to
> intelligently wait for the remote (RT work doing) CPU to finish
> executing kernel code, without polling or so.
it's basically a cheap IPI being inserted on the remote CPU.
We need the TIF_RCU_QS callback not just to wait intelligently, but
mainly to elapse a grace period, otherwise synchronize_rcu() might not
ever make progress: think a SCHED_FIFO task doing some kernel work,
synchronize_rcu() stumbling upon it - but the SCHED_FIFO task
otherwise never scheduling and never getting any timer irqs either,
and thus never entering quiescent state.
(Cc:-ed Paul too, he might be interested in this as well.)
Thanks,
Ingo
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