From: Boqun Feng <boqun.feng@gmail.com>
To: peterz@infradead.org
Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org,
stern@rowland.harvard.edu, parri.andrea@gmail.com,
will@kernel.org, npiggin@gmail.com, dhowells@redhat.com,
j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com
Subject: Re: [PATCH kcsan 6/9] tools/memory-model: Expand the cheatsheet.txt notion of relaxed
Date: Wed, 2 Sep 2020 20:37:15 +0800 [thread overview]
Message-ID: <20200902123715.GD49492@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> (raw)
In-Reply-To: <20200902101412.GC1362448@hirez.programming.kicks-ass.net>
On Wed, Sep 02, 2020 at 12:14:12PM +0200, peterz@infradead.org 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@kernel.org wrote:
> > > From: "Paul E. McKenney" <paulmck@kernel.org>
> > >
> > > This commit adds a key entry enumerating the various types of relaxed
> > > operations.
> > >
> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > > ---
> > > 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
next prev parent reply other threads:[~2020-09-02 12:37 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 18:20 [PATCH memory-model 0/9] LKMM updates for v5.10 Paul E. McKenney
2020-08-31 18:20 ` [PATCH kcsan 1/9] docs: fix references for DMA*.txt files paulmck
2020-08-31 18:20 ` [PATCH kcsan 2/9] Replace HTTP links with HTTPS ones: LKMM paulmck
2020-08-31 18:20 ` [PATCH kcsan 3/9] tools/memory-model: Update recipes.txt prime_numbers.c path paulmck
2020-08-31 18:20 ` [PATCH kcsan 4/9] tools/memory-model: Improve litmus-test documentation paulmck
2020-08-31 18:20 ` [PATCH kcsan 5/9] tools/memory-model: Add a simple entry point document paulmck
2020-08-31 18:20 ` [PATCH kcsan 6/9] tools/memory-model: Expand the cheatsheet.txt notion of relaxed paulmck
2020-09-02 3:54 ` Boqun Feng
2020-09-02 10:14 ` peterz
2020-09-02 12:37 ` Boqun Feng [this message]
2020-09-02 12:47 ` peterz
2020-09-03 23:30 ` Paul E. McKenney
2020-09-04 0:59 ` Boqun Feng
2020-09-04 2:39 ` Paul E. McKenney
2020-09-04 2:47 ` Boqun Feng
2020-09-04 19:56 ` Paul E. McKenney
2020-08-31 18:20 ` [PATCH kcsan 7/9] tools/memory-model: Move Documentation description to Documentation/README paulmck
2020-08-31 18:20 ` [PATCH kcsan 8/9] tools/memory-model: Document categories of ordering primitives paulmck
2020-08-31 22:34 ` Akira Yokosawa
2020-08-31 23:12 ` Paul E. McKenney
2020-09-01 1:23 ` Alan Stern
2020-09-01 2:58 ` Paul E. McKenney
2020-08-31 18:20 ` [PATCH kcsan 9/9] tools/memory-model: Document locking corner cases paulmck
2020-08-31 20:17 ` Alan Stern
2020-08-31 21:47 ` Paul E. McKenney
2020-09-01 1:45 ` Alan Stern
2020-09-01 17:04 ` Paul E. McKenney
2020-09-01 20:11 ` Alan Stern
2020-09-03 23:45 ` Paul E. McKenney
2020-09-04 19:52 ` Alan Stern
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