| | Date | Wed, 2 Nov 2011 21:47:44 -0700 | | From | Josh Triplett <> | | Subject | Re: [PATCH RFC tip/core/rcu 27/28] rcu: Allow dyntick-idle mode for CPUs with callbacks |
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On Wed, Nov 02, 2011 at 01:30:48PM -0700, Paul E. McKenney wrote: > /* > - * Check to see if any future RCU-related work will need to be done > - * by the current CPU, even if none need be done immediately, returning > - * 1 if so. This function is part of the RCU implementation; it is -not- > - * an exported member of the RCU API. > + * Allow the CPU to enter dyntick-idle mode if either: (1) There are no > + * callbacks on this CPU, (2) this CPU has not yet attempted to enter > + * dyntick-idle mode, and (3) this CPU is in the process of attempting to > + * enter dyntick-idle mode. Otherwise, if we have recently tried and failed
This sentence doesn't quite work; "if either...and..." should become "either...or" or "if...and".
> + * to enter dyntick-idle mode, we refuse to try to enter it. After all, > + * it is better to incur scheduling-clock interrupts than to spin > + * continuously for the same time duration! > + */ > +int rcu_needs_cpu(int cpu) > +{ > + /* If no callbacks, RCU doesn't need the CPU. */ > + if (!rcu_cpu_has_callbacks(cpu)) > + return 0; > + /* Otherwise, RCU needs the CPU only if it recently tried and failed. */ > + return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies;
Sigh, one more use of jiffies. :(
- Josh Triplett
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