diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2023-10-20 11:04:27 -0700 |
|---|---|---|
| committer | Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com> | 2023-12-14 01:16:28 +0530 |
| commit | ad9446302919ee3a646ad667a9ea15f992685dca (patch) | |
| tree | 2aebbabf056054d7f910dde708cc2985a1e7017c | |
| parent | c49956be75152a533787f5daa06ef4b710207499 (diff) | |
doc: Clarify historical disclaimers in memory-barriers.txt
This commit makes it clear that the reason that these sections are
historical is that smp_read_barrier_depends() is no more. It also
removes the point about comparison operations, given that there are
other optimizations that can break address dependencies.
Suggested-by: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Will Deacon <will@kernel.org>
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: Akira Yokosawa <akiyks@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: <linux-arch@vger.kernel.org>
Cc: <linux-doc@vger.kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
| -rw-r--r-- | Documentation/memory-barriers.txt | 17 |
1 files changed, 10 insertions, 7 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index d414e145f912..4202174a6262 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -396,10 +396,11 @@ Memory barriers come in four basic varieties: (2) Address-dependency barriers (historical). - [!] This section is marked as HISTORICAL: For more up-to-date - information, including how compiler transformations related to pointer - comparisons can sometimes cause problems, see - Documentation/RCU/rcu_dereference.rst. + [!] This section is marked as HISTORICAL: it covers the long-obsolete + smp_read_barrier_depends() macro, the semantics of which are now + implicit in all marked accesses. For more up-to-date information, + including how compiler transformations can sometimes break address + dependencies, see Documentation/RCU/rcu_dereference.rst. An address-dependency barrier is a weaker form of read barrier. In the case where two loads are performed such that the second depends on the @@ -560,9 +561,11 @@ There are certain things that the Linux kernel memory barriers do not guarantee: ADDRESS-DEPENDENCY BARRIERS (HISTORICAL) ---------------------------------------- -[!] This section is marked as HISTORICAL: For more up-to-date information, -including how compiler transformations related to pointer comparisons can -sometimes cause problems, see Documentation/RCU/rcu_dereference.rst. +[!] This section is marked as HISTORICAL: it covers the long-obsolete +smp_read_barrier_depends() macro, the semantics of which are now implicit +in all marked accesses. For more up-to-date information, including +how compiler transformations can sometimes break address dependencies, +see Documentation/RCU/rcu_dereference.rst. As of v4.15 of the Linux kernel, an smp_mb() was added to READ_ONCE() for DEC Alpha, which means that about the only people who need to pay attention |