On Wed, Oct 31, 2018 at 03:57:21PM -0700, Andy Lutomirski wrote: > > On Oct 31, 2018, at 2:00 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > >> On Wed, Oct 31, 2018 at 01:36:48PM -0700, Andy Lutomirski wrote: > >> This stuff is called *rare* write for a reason. Do we really want to > >> allow atomics beyond just store-release? Taking a big lock and then > >> writing in the right order should cover everything, no? > > > > Ah, so no. That naming is very misleading. > > > > We modify page-tables a _lot_. The point is that only a few sanctioned > > sites are allowed writing to it, not everybody. > > > > I _think_ the use-case for atomics is updating the reference counts of > > objects that are in this write-rare domain. But I'm not entirely clear > > on that myself either. I just really want to avoid duplicating that > > stuff. > > Sounds nuts. Doing a rare-write is many hundreds of cycles at best. Yes, which is why I'm somewhat sceptical of the whole endeavour.
