On Wed, Feb 07, 2018 at 05:45:13PM +0100, Jesper Dangaard Brouer wrote: > On Wed, 7 Feb 2018 08:57:00 -0500 > Steven Rostedt <rost...@goodmis.org> wrote: > > To me kvfree() is a special case and should not be used by RCU as a > > generic function. That would make RCU and MM much more coupled than > > necessary. > > For the record, I fully agree with Steve here. > > And being a performance "fanatic" I don't like to have the extra branch > (and compares) in the free code path... but it's a MM-decision (and > sometimes you should not listen to "fanatics" ;-))
While free_rcu() is not withut its performance requirements, I think it's currently dominated by cache misses and not by branches. By the time RCU gets to run callbacks, memory is certainly L1/L2 cache-cold and probably L3 cache-cold. Also calling the callback functions is utterly impossible for the branch predictor.
