On Wed, Sep 02, 2020 at 12:14:12PM +0200, peterz@xxxxxxxxxxxxx wrote: > On Wed, Sep 02, 2020 at 11:54:48AM +0800, Boqun Feng wrote: > > On Mon, Aug 31, 2020 at 11:20:34AM -0700, paulmck@xxxxxxxxxx wrote: > > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > > > > > This commit adds a key entry enumerating the various types of relaxed > > > operations. > > > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > > --- > > > 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. > IIUC, the DW colomn stands for whether the corresponding operation (in this case, it's atomic_set()) is ordered any write that depends on this operation. I don't think there is a write->write dependency, so DW for atomic_set() should not be Y, just as the DW for WRITE_ONCE(). > > 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 ? Agreed. Probably we should fold those two operations into "Load" and "Store" cases. Regards, Boqun
