On Sat, Apr 07, 2018 at 10:47:32AM +0200, Peter Zijlstra wrote: > On Fri, Apr 06, 2018 at 02:09:53PM -0700, Paul E. McKenney wrote: > > It would indeed be good to not be in the position of having to trade off > > forward-progress guarantees against performance, but that does appear to > > be where we are at the moment. > > Depends of course on how unfair cmpxchg is. On x86 we trade one cmpxchg > loop for another so the patch doesn't cure anything at all there. And > our cmpxchg has 'some' hardware fairness to it. > > So while the patch is 'good' for platforms that have native fetch-or, > it doesn't help (or in our case even hurts) those that do not.
Might need different implementations for different architectures, then. Or take advantage of the fact that x86 can do a native fetch-or to the topmost bit, if that helps. Thanx, Paul