On Tue, Dec 05, 2017 at 10:17:35PM +0100, Peter Zijlstra wrote: > On Tue, Dec 05, 2017 at 10:28:38PM +0200, Michael S. Tsirkin wrote: > > On Tue, Dec 05, 2017 at 08:57:52PM +0100, Peter Zijlstra wrote: > > > On Tue, Dec 05, 2017 at 09:51:48PM +0200, Michael S. Tsirkin wrote: > > > > > > WRITE_ONCE(obj->val, 1); > > > > > > smp_wmb(); > > > > > > WRITE_ONCE(*foo, obj); > > > > > > > > > > I believe Peter was instead suggesting: > > > > > > > > > > WRITE_ONCE(obj->val, 1); > > > > > smp_store_release(foo, obj); > > > > > > > > Isn't that more expensive though? > > > > > > Depends on the architecture. The only architecture where it is more > > > expensive and people actually still care about is ARM I think. > > > > Right. Why should I use the more expensive smp_store_release then? > > Because it makes more sense. Memory ordering is hard enough, don't make > it harder still if you don't have to. I suspect I have to - ptr_ring is a very low level construct used by netowrking on data path so making it a bit more complicated for a bit of performance is probably justified. -- MST
