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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-11-27 09:20:40 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-12-05 11:57:53 -0800 |
| commit | 9ad3c143d7d6942c66f27bc6c18f5df638f70aff (patch) | |
| tree | b0b52f72cd5d03677b2d643feaaa7220aa109f29 /Documentation/memory-barriers.txt | |
| parent | 98c1ec7cefaadbf65680d116c3d8612b93a841a0 (diff) | |
| download | lwn-9ad3c143d7d6942c66f27bc6c18f5df638f70aff.tar.gz lwn-9ad3c143d7d6942c66f27bc6c18f5df638f70aff.zip | |
doc: De-emphasize smp_read_barrier_depends
This commit keeps only the historical and low-level discussion of
smp_read_barrier_depends().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
Diffstat (limited to 'Documentation/memory-barriers.txt')
| -rw-r--r-- | Documentation/memory-barriers.txt | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 13fd35b6a597..a863009849a3 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1818,7 +1818,7 @@ The Linux kernel has eight basic CPU memory barriers: GENERAL mb() smp_mb() WRITE wmb() smp_wmb() READ rmb() smp_rmb() - DATA DEPENDENCY read_barrier_depends() smp_read_barrier_depends() + DATA DEPENDENCY READ_ONCE() All memory barriers except the data dependency barriers imply a compiler @@ -2867,7 +2867,10 @@ access depends on a read, not all do, so it may not be relied on. Other CPUs may also have split caches, but must coordinate between the various cachelets for normal memory accesses. The semantics of the Alpha removes the -need for coordination in the absence of memory barriers. +need for hardware coordination in the absence of memory barriers, which +permitted Alpha to sport higher CPU clock rates back in the day. However, +please note that smp_read_barrier_depends() should not be used except in +Alpha arch-specific code and within the READ_ONCE() macro. CACHE COHERENCY VS DMA |