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tools/memory-model: Update the informal documentation

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The formal memory consistency model has added support for plain accesses
(and data races).  While updating the informal documentation to describe
this addition to the model is highly desirable and important future work,
update the informal documentation to at least acknowledge such addition.

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
This commit is contained in:
Andrea Parri
2019-06-29 23:10:44 +02:00
committed by Paul E. McKenney
parent 6240973e56
commit 6738ff85c3
2 changed files with 27 additions and 32 deletions
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tools/memory-model/README
+8 -8
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@@ -167,15 +167,15 @@ scripts Various scripts, see scripts/README.
LIMITATIONS
===========
The Linux-kernel memory model has the following limitations:
The Linux-kernel memory model (LKMM) has the following limitations:
1. Compiler optimizations are not modeled. Of course, the use
of READ_ONCE() and WRITE_ONCE() limits the compiler's ability
to optimize, but there is Linux-kernel code that uses bare C
memory accesses. Handling this code is on the to-do list.
For more information, see Documentation/explanation.txt (in
particular, the "THE PROGRAM ORDER RELATION: po AND po-loc"
and "A WARNING" sections).
1. Compiler optimizations are not accurately modeled. Of course,
the use of READ_ONCE() and WRITE_ONCE() limits the compiler's
ability to optimize, but under some circumstances it is possible
for the compiler to undermine the memory model. For more
information, see Documentation/explanation.txt (in particular,
the "THE PROGRAM ORDER RELATION: po AND po-loc" and "A WARNING"
sections).
Note that this limitation in turn limits LKMM's ability to
accurately model address, control, and data dependencies.