On Wed, 7 Feb 2018 10:10:55 -0800 Matthew Wilcox <wi...@infradead.org> wrote:
> > For the record, I fully agree with Steve here. Thanks, but... > > > > 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. I agree with Matthew. This is far from any fast path. A few extra branches isn't going to hurt anything here as it's mostly just garbage collection. With or without the Spectre fixes. -- Steve
