Re: [patch 08/23] dynticks: prepare the RCU code

From: Ingo Molnar
Date: Sat Sep 30 2006 - 09:50:37 EST

* Dipankar Sarma <dipankar@xxxxxxxxxx> wrote:

> It is duplicating code. That can be easily fixed, but we need to
> figure out what we really want from RCU when we are about to switch
> off the ticks. It is hard if you want to finish off all the pending
> RCUs and go to nohz state. Can you live with backing out if there are
> pending RCUs ?

the thing is that when we go idle we /want/ to process whatever delayed
work there might be - rate limited or not. Do you agree with that
approach? I consider this a performance feature as well: this way we can
utilize otherwise lost idle time. It is not a problem that we dont
'batch' this processing: we are really idle and we've got free cycles to
burn. We could even do an RCU processing loop that immediately breaks
out if need_resched() gets set [by an IRQ or by another CPU].

secondly, i think i saw functionality problems when RCU was not
completed before going idle - for example synchronize_rcu() on another
CPU would hang.

what approach would you suggest to achieve these goals?

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