On Thu, Jul 12, 2018 at 09:52:42PM +0200, Andrea Parri wrote: > On Thu, Jul 12, 2018 at 11:10:58AM -0700, Linus Torvalds wrote: > > On Thu, Jul 12, 2018 at 11:05 AM Peter Zijlstra <pet...@infradead.org> > > wrote: > > > > > > The locking pattern is fairly simple and shows where RCpc comes apart > > > from expectation real nice. > > > > So who does RCpc right now for the unlock-lock sequence? Somebody > > mentioned powerpc. Anybody else? > > powerpc have RCtso (and RCpc) but not RCsc unlock-lock, according to the > following indeed original terminology: > > - RCsc unlock-lock MUST ORDER: > > a) the WRITE and the READ below: > > WRITE x=1 > UNLOCK s > LOCK s > READ y > > as in a store-buffering test; > > b) the two WRITEs below: > > WRITE x=1 > UNLOCK s > LOCK s > WRITE y=1 > > as in a message-passing test; > > c) the two READs below: > > READ x > UNLOCK s > LOCK s > READ y > > as in a message-passing test; > > d) the READ and the WRITE below: > > READ x > UNLOCK s > LOCK s > WRITE y > > as in a load-buffering test; > > - RCtso unlock-lock MUST ORDER b), c), d) above. > > - RCpc unlock-lock MUST ORDER none of the above. > > AFAICT, all arch _in_ the current implementation have RCtso unlock-lock. > > > > > > How nasty would be be to make powerpc conform? I will always advocate > > tighter locking and ordering rules over looser ones.. > > A simple answer is right above (place a sync somewhere in the sequence); > for benchmark results, I must defer...
Sorry, not sure why but I did intend "conform to RCsc" here. > > Andrea > > > > > > Linus
