On Wed, Sep 02, 2020 at 11:54:48AM +0800, Boqun Feng wrote: > On Mon, Aug 31, 2020 at 11:20:34AM -0700, [email protected] wrote: > > From: "Paul E. McKenney" <[email protected]> > > > > This commit adds a key entry enumerating the various types of relaxed > > operations. > > > > Signed-off-by: Paul E. McKenney <[email protected]> > > --- > > tools/memory-model/Documentation/cheatsheet.txt | 27 > > ++++++++++++++----------- > > 1 file changed, 15 insertions(+), 12 deletions(-) > > > > diff --git a/tools/memory-model/Documentation/cheatsheet.txt > > b/tools/memory-model/Documentation/cheatsheet.txt > > index 33ba98d..31b814d 100644 > > --- a/tools/memory-model/Documentation/cheatsheet.txt > > +++ b/tools/memory-model/Documentation/cheatsheet.txt > > @@ -5,7 +5,7 @@ > > > > Store, e.g., WRITE_ONCE() Y > > Y > > Load, e.g., READ_ONCE() Y Y Y > > Y > > -Unsuccessful RMW operation Y Y Y > > Y > > +Relaxed operation Y Y Y > > Y > > rcu_dereference() Y Y Y > > Y > > Successful *_acquire() R Y Y Y Y Y > > Y > > Successful *_release() C Y Y Y W > > Y > > @@ -17,14 +17,17 @@ smp_mb__before_atomic() CP Y Y Y > > a a a a Y > > smp_mb__after_atomic() CP a a Y Y Y Y Y Y > > > > > > -Key: C: Ordering is cumulative > > - P: Ordering propagates > > - R: Read, for example, READ_ONCE(), or read portion of RMW > > - W: Write, for example, WRITE_ONCE(), or write portion of RMW > > - Y: Provides ordering > > - a: Provides ordering given intervening RMW atomic operation > > - DR: Dependent read (address dependency) > > - DW: Dependent write (address, data, or control dependency) > > - RMW: Atomic read-modify-write operation > > - SELF: Orders self, as opposed to accesses before and/or after > > - SV: Orders later accesses to the same variable > > +Key: Relaxed: A relaxed operation is either a *_relaxed() RMW > > + operation, an unsuccessful RMW operation, or one of > > + the atomic_read() and atomic_set() family of operations. > > To be accurate, atomic_set() doesn't return any value, so it cannot be > ordered against DR and DW ;-)
Surely DW is valid for any store. > I think we can split the Relaxed family into two groups: > > void Relaxed: atomic_set() or atomic RMW operations that don't return > any value (e.g atomic_inc()) > > non-void Relaxed: a *_relaxed() RMW operation, an unsuccessful RMW > operation, or atomic_read(). > > And "void Relaxed" is similar to WRITE_ONCE(), only has "Self" and "SV" > equal "Y", while "non-void Relaxed" plays the same rule as "Relaxed" > in this patch. > > Thoughts? I get confused by the mention of all this atomic_read() atomic_set() crud in the first place, why are they called out specifically from any other regular load/store ?
