Messages in this thread | | | Date | Tue, 5 May 2015 12:48:34 +0200 | From | Peter Zijlstra <> | Subject | Re: question about RCU dynticks_nesting |
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On Mon, May 04, 2015 at 03:00:44PM -0400, Rik van Riel wrote: In case of the non-preemptible RCU, we could easily also > increase current->rcu_read_lock_nesting at the same time > we increase the preempt counter, and use that as the > indicator to test whether the cpu is in an extended > rcu quiescent state. That way there would be no extra > overhead at syscall entry or exit at all. The trick > would be getting the preempt count and the rcu read > lock nesting count in the same cache line for each task.
Can't do that. Remember, on x86 we have per-cpu preempt count, and your rcu_read_lock_nesting is per task.
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