On Wed, 3 Aug 2016, Andy Lutomirski wrote: > > Well, a CMPXCHG without LOCK prefix isn't all that expensive on x86. > > > > It is however on PPC and possibly other architectures, so in name of > > simplicity supporting only the one variant makes sense. > > > > I wouldn't want to depend on CMPXCHG. But imagine we had primitives > that were narrower than the full abort-on-preemption primitive. > Specifically, suppose we had abort if (actual cpu != expected_cpu || > *aptr != aval). We could do things like: >
The latency issues that are addressed by restartable sequences require minimim instruction overhead. Lockless CMPXCHG is very important in that area and I would not simply remove it from consideration.
