Messages in this thread | | | Date | Thu, 12 Jul 2018 21:52:42 +0200 | From | Andrea Parri <> | Subject | Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire |
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On Thu, Jul 12, 2018 at 11:10:58AM -0700, Linus Torvalds wrote: > On Thu, Jul 12, 2018 at 11:05 AM Peter Zijlstra <peterz@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...
Andrea
> > Linus
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