On Tue, 2013-06-18 at 18:53 -0700, Paul E. McKenney wrote: > On Tue, Jun 18, 2013 at 05:37:42PM +0200, Torvald Riegel wrote: > > On Tue, 2013-06-18 at 07:50 -0700, Paul E. McKenney wrote: > > > First, I am not a fan of SC, mostly because there don't seem to be many > > > (any?) production-quality algorithms that need SC. But if you really > > > want to take a parallel-programming trip back to the 1980s, let's go! ;-) > > > > Dekker-style mutual exclusion is useful for things like read-mostly > > multiple-reader single-writer locks, or similar "asymmetric" cases of > > synchronization. SC fences are needed for this. > > They definitely need Power hwsync rather than lwsync, but they need > fewer fences than would be emitted by slavishly following either of the > SC recipes for Power. (Another example needing store-to-load ordering > is hazard pointers.)
The C++11 seq-cst fence expands to hwsync; combined with a relaxed store / load, that should be minimal. Or are you saying that on Power, there is a weaker HW barrier available that still constrains store-load reordering sufficiently? Torvald
