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Date: Fri, 22 Nov 2013 04:31:17 -0800
From: tip-bot for Ingo Molnar <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
tglx@...utronix.de
Subject: [tip:core/locking] Documentation/memory-barriers.txt:
Fix a typo in the data dependency description
Commit-ID: e0edc78f25c020dea66742c05a7fbcb2ff3df629
Gitweb: http://git.kernel.org/tip/e0edc78f25c020dea66742c05a7fbcb2ff3df629
Author: Ingo Molnar <mingo@...nel.org>
AuthorDate: Fri, 22 Nov 2013 11:24:53 +0100
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 22 Nov 2013 11:46:12 +0100
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@...llo.nl>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-gncea9cb8igosblizfqMXrie@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
Documentation/memory-barriers.txt | 42 +++++++++++++++++++--------------------
1 file changed, 21 insertions(+), 21 deletions(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index c8c42e6..020cccd 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -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>
--
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