On Thu, Oct 08, 2015 at 02:44:39PM -0700, Paul E. McKenney wrote: > > > > I am with Peter -- we do need the benchmark results for PPC. > > > > > > Urgh, sorry guys. I have been slowly doing some benchmarks, but time is not > > > plentiful at the moment. > > > > > > If we do a straight lwsync -> sync conversion for unlock it looks like that > > > will cost us ~4.2% on Anton's standard context switch benchmark. > > > > And that does not seem to agree with Paul's smp_mb__after_unlock_lock() > > usage and would not be sufficient for the same (as of yet unexplained) > > reason. > > > > Why does it matter which of the LOCK or UNLOCK gets promoted to full > > barrier on PPC in order to become RCsc? > > You could do either. However, as I understand it, there is hardware for > which bc;isync is faster than lwsync. For such hardware, it is cheaper > to upgrade the unlock from lwsync to sync than to upgrade the lock from > bc;isync to sync. If I recall correctly, the kernel rewrites itself at > boot to select whichever of lwsync or bc;isync is better for the hardware > at hand. Fair enough. I'll go wake up and think about the other issue ;-) -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
