Messages in this thread | | | Date | Tue, 5 May 2015 05:34:46 -0700 | From | "Paul E. McKenney" <> | Subject | Re: question about RCU dynticks_nesting |
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On Tue, May 05, 2015 at 12:53:46PM +0200, Peter Zijlstra wrote: > On Mon, May 04, 2015 at 12:39:23PM -0700, Paul E. McKenney wrote: > > But in non-preemptible RCU, we have PREEMPT=n, so there is no preempt > > counter in production kernels. Even if there was, we have to sample this > > on other CPUs, so the overhead of preempt_disable() and preempt_enable() > > would be where kernel entry/exit is, so I expect that this would be a > > net loss in overall performance. > > We unconditionally have the preempt_count, its just not used much for > PREEMPT_COUNT=n kernels.
We have the field, you mean? I might be missing something, but it still appears to me thta preempt_disable() does nothing for PREEMPT=n kernels. So what am I missing?
Thanx, Paul
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