On Mon, Aug 11, 2014 at 03:49:03PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> > > In theory, synchronize_sched() requires a read-side critical section to > order against. In practice, preemption can be thought of as being > disabled across every machine instruction. So this commit removes > the redundant preempt_disable() from rcu_note_voluntary_context_switch().
> #define rcu_note_voluntary_context_switch(t) \
> do { \
> - preempt_disable(); /* Exclude synchronize_sched(); */ \
> if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \
> ACCESS_ONCE((t)->rcu_tasks_holdout) = 0; \
> - preempt_enable(); \
> } while (0)
But that's more than 1 instruction.
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