Hi Joel, On Sat, Jul 27, 2019 at 08:00:31PM -0400, Joel Fernandes (Google) wrote: > This lkmm example should describe an additional rfe link between P1's > store to y and P2's load of y, which should be critical to establishing > the ordering resulting in the ->prop ordering on P0. IOW, there are 2 rfe > links, not one. > > Correct these in the docs to make the ->prop ordering in P0 more clear. > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > --- > tools/memory-model/Documentation/explanation.txt | 16 +++++++++------- > 1 file changed, 9 insertions(+), 7 deletions(-) > > diff --git a/tools/memory-model/Documentation/explanation.txt b/tools/memory-model/Documentation/explanation.txt > index 68caa9a976d0..6c0dfaac7f04 100644 > --- a/tools/memory-model/Documentation/explanation.txt > +++ b/tools/memory-model/Documentation/explanation.txt > @@ -1302,8 +1302,8 @@ followed by an arbitrary number of cumul-fence links, ending with an > rfe link. You can concoct more exotic examples, containing more than > one fence, although this quickly leads to diminishing returns in terms > of complexity. For instance, here's an example containing a coe link > -followed by two fences and an rfe link, utilizing the fact that > -release fences are A-cumulative: > +followed by a fence, an rfe link, another fence and and a final rfe link, > +utilizing the fact that release fences are A-cumulative: > This part looks good to me. > int x, y, z; > > @@ -1334,11 +1334,13 @@ If x = 2, r0 = 1, and r2 = 1 after this code runs then there is a prop > link from P0's store to its load. This is because P0's store gets > overwritten by P1's store since x = 2 at the end (a coe link), the > smp_wmb() ensures that P1's store to x propagates to P2 before the > -store to y does (the first fence), the store to y propagates to P2 > -before P2's load and store execute, P2's smp_store_release() > -guarantees that the stores to x and y both propagate to P0 before the > -store to z does (the second fence), and P0's load executes after the > -store to z has propagated to P0 (an rfe link). > +store to y does (the first fence), P2's store to y happens before P2's > +load of y (rfe link), P2's smp_store_release() ensures that P2's load > +of y executes before P2's store of z (second fence), which also would > +imply that stores to x and y happen before the smp_store_release(), which I think it's more accurate to say: "imply that stores to x and y progagates to P2 before the smp_store_release()" , because by definition the propagation ordering that smp_store_release() guarantees only works with stores that already propagated to the CPU executing it, not the stores that execute/happen before. With that, feel free to add: Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx> Regards, Boqun > +means that P2's smp_store_release() will propagate stores to x and y to all > +CPUs before the store to z does (A-cumulative property of this fence). > +Finally P0's load executes after store to z has propagated to P0 (rfe link). > > In summary, the fact that the hb relation links memory access events > in the order they execute means that it must not have cycles. This > -- > 2.22.0.709.g102302147b-goog >
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