Messages in this thread | | | Date | Wed, 24 Jun 2015 09:50:50 -0700 | From | Dave Hansen <> | Subject | Re: [RFC][PATCH] fs: optimize inotify/fsnotify code for unwatched files |
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On 06/22/2015 05:26 PM, Paul E. McKenney wrote: > OK, here is an experimental patch that provides a fast-readers variant > of RCU, forward-ported from v3.3. Because we didn't have call_srcu() > and srcu_barrier() back then, it is not a drop-in replacement for SRCU, > so you need to adapt the code to the API, which means putting an "fr" > in front of the "srcu" in the API members. > > Understood on the overhead of the memory-barrier instruction showing > up consistently. My point was instead that getting rid of this > memory-barrier instruction does not come for free, as it greatly > increases the latency of synchronize_frsrcu(). In a real workload, > it is entirely possible that the savings from eliminating the memory > barrier are overwhelmed by the increased grace-period latency. > > Anyway, the patch is below. Very lightly tested.
This does give a very similar performance boost as the other optimization I posted. I measured this patch to boost the writes/second by 11.0% while my previous optimization did 10.8%.
I don't think this workload will see any of the overhead of the synchronize_frsrcu(), though, but this helps confirm the source of the overhead.
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