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Documentation/memory-barriers.txt: Fix a typo in the data dependency description 

This typo has been there forever, it is 7.5 years old, looks like this
section of our memory ordering documentation is a place where most eyes
are glazed over already ;-)

[ Also fix some stray spaces and stray tabs while at it, shrinking the
  file by 49 bytes. Visual output unchanged. ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-gncea9cb8igosblizfqMXrie@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar 2013-11-22 11:24:53 +01:00
parent b4789b8e6b
commit e0edc78f25
1 changed files with 21 additions and 21 deletions
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42
Documentation/memory-barriers.txt
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@ -500,7 +500,7 @@ odd-numbered bank is idle, one can see the new value of the pointer P (&B),
but the old value of the variable B (2).
Another example of where data dependency barriers might by required is where a
Another example of where data dependency barriers might be required is where a
number is read from memory and then used to calculate the index for an array
access:
@ -882,12 +882,12 @@ cache it for later use.
Consider:
CPU 1 CPU 2
CPU 1 CPU 2
======================= =======================
LOAD B
DIVIDE } Divide instructions generally
DIVIDE } take a long time to perform
LOAD A
LOAD B
DIVIDE } Divide instructions generally
DIVIDE } take a long time to perform
LOAD A
Which might appear as this:
@ -910,13 +910,13 @@ Which might appear as this:
Placing a read barrier or a data dependency barrier just before the second
load:
CPU 1 CPU 2
CPU 1 CPU 2
======================= =======================
LOAD B
DIVIDE
DIVIDE
LOAD B
DIVIDE
DIVIDE
<read barrier>
LOAD A
LOAD A
will force any value speculatively obtained to be reconsidered to an extent
dependent on the type of barrier used. If there was no change made to the
@ -1887,8 +1887,8 @@ functions:
space should suffice for PCI.
[*] NOTE! attempting to load from the same location as was written to may
cause a malfunction - consider the 16550 Rx/Tx serial registers for
example.
cause a malfunction - consider the 16550 Rx/Tx serial registers for
example.
Used with prefetchable I/O memory, an mmiowb() barrier may be required to
force stores to be ordered.
@ -1955,19 +1955,19 @@ barriers for the most part act at the interface between the CPU and its cache
:
+--------+ +--------+ : +--------+ +-----------+
| | | | : | | | | +--------+
| CPU | | Memory | : | CPU | | | | |
| Core |--->| Access |----->| Cache |<-->| | | |
| CPU | | Memory | : | CPU | | | | |
| Core |--->| Access |----->| Cache |<-->| | | |
| | | Queue | : | | | |--->| Memory |
| | | | : | | | | | |
+--------+ +--------+ : +--------+ | | | |
| | | | : | | | | | |
+--------+ +--------+ : +--------+ | | | |
: | Cache | +--------+
: | Coherency |
: | Mechanism | +--------+
+--------+ +--------+ : +--------+ | | | |
| | | | : | | | | | |
| CPU | | Memory | : | CPU | | |--->| Device |
| Core |--->| Access |----->| Cache |<-->| | | |
| | | Queue | : | | | | | |
| Core |--->| Access |----->| Cache |<-->| | | |
| | | Queue | : | | | | | |
| | | | : | | | | +--------+
+--------+ +--------+ : +--------+ +-----------+
:
@ -2090,7 +2090,7 @@ CPU's caches by some other cache event:
p = &v; q = p;
<D:request p>
<B:modify p=&v> <D:commit p=&v>
<D:read p>
<D:read p>
x = *q;
<C:read *q> Reads from v before v updated in cache
<C:unbusy>
@ -2115,7 +2115,7 @@ queue before processing any further requests:
p = &v; q = p;
<D:request p>
<B:modify p=&v> <D:commit p=&v>
<D:read p>
<D:read p>
smp_read_barrier_depends()
<C:unbusy>
<C:commit v=2>