* [PATCH] doc: memory-barriers.txt: Correct example for reorderings
@ 2014-08-25 13:08 Pranith Kumar
[not found] ` <53FF8B77.7000103@infradead.org>
0 siblings, 1 reply; 6+ messages in thread
From: Pranith Kumar @ 2014-08-25 13:08 UTC (permalink / raw)
To: Randy Dunlap, open list:DOCUMENTATION, open list
Correct the example of memory orderings in memory-barriers.txt
Commit 615cc2c9cf95 "Documentation/memory-barriers.txt: fix important typo re
memory barriers" changed the assignment to x and y. Change the rest of the
example to match this change.
Reported-by: Ganesh Rapolu <ganesh.rapolu@hotmail.com>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
Documentation/memory-barriers.txt | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index a4de88f..cf31875 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -121,22 +121,22 @@ For example, consider the following sequence of events:
The set of accesses as seen by the memory system in the middle can be arranged
in 24 different combinations:
- STORE A=3, STORE B=4, x=LOAD A->3, y=LOAD B->4
- STORE A=3, STORE B=4, y=LOAD B->4, x=LOAD A->3
- STORE A=3, x=LOAD A->3, STORE B=4, y=LOAD B->4
- STORE A=3, x=LOAD A->3, y=LOAD B->2, STORE B=4
- STORE A=3, y=LOAD B->2, STORE B=4, x=LOAD A->3
- STORE A=3, y=LOAD B->2, x=LOAD A->3, STORE B=4
- STORE B=4, STORE A=3, x=LOAD A->3, y=LOAD B->4
+ STORE A=3, STORE B=4, x=LOAD B->4, y=LOAD A->3
+ STORE A=3, STORE B=4, y=LOAD A->3, x=LOAD B->4
+ STORE B=4, x=LOAD B->4, STORE A=3, y=LOAD A->3
+ STORE A=3, x=LOAD B->2, y=LOAD A->3, STORE B=4
+ STORE B=4, y=LOAD A->1, STORE A=3, x=LOAD B->4
+ STORE B=4, y=LOAD A->1, x=LOAD B->4, STORE A=3
+ STORE B=4, STORE A=3, x=LOAD B->4, y=LOAD A->3
STORE B=4, ...
...
and can thus result in four different combinations of values:
- x == 1, y == 2
- x == 1, y == 4
- x == 3, y == 2
- x == 3, y == 4
+ x == 2, y == 1
+ x == 2, y == 3
+ x == 4, y == 1
+ x == 4, y == 3
Furthermore, the stores committed by a CPU to the memory system may not be
--
1.9.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] doc: memory-barriers.txt: Correct example for reorderings
[not found] ` <20140828210010.GM5001@linux.vnet.ibm.com>
@ 2014-08-28 21:15 ` Pranith Kumar
2014-08-28 21:39 ` Paul E. McKenney
0 siblings, 1 reply; 6+ messages in thread
From: Pranith Kumar @ 2014-08-28 21:15 UTC (permalink / raw)
To: Paul McKenney; +Cc: Randy Dunlap, open list:DOCUMENTATION, LKML
On Thu, Aug 28, 2014 at 5:00 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>
> I am really confused by the ordering of the new lines, as I would have
> expected the "x"s to be replaced with "y"s and vice versa. But the
> ordering of the various combinations does not matter, and each line
> looks OK.
>
Since x = A was replaced by x = B and y = B was replaced by y = A, I
just converted all x = load A to x = load B. Similarly for y. I think
we can do either this or as you suggested replacing x's with y's.
--
Pranith
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] doc: memory-barriers.txt: Correct example for reorderings
2014-08-28 21:15 ` Pranith Kumar
@ 2014-08-28 21:39 ` Paul E. McKenney
2014-08-28 21:45 ` Pranith Kumar
0 siblings, 1 reply; 6+ messages in thread
From: Paul E. McKenney @ 2014-08-28 21:39 UTC (permalink / raw)
To: Pranith Kumar; +Cc: Randy Dunlap, open list:DOCUMENTATION, LKML
On Thu, Aug 28, 2014 at 05:15:50PM -0400, Pranith Kumar wrote:
> On Thu, Aug 28, 2014 at 5:00 PM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> >
> > I am really confused by the ordering of the new lines, as I would have
> > expected the "x"s to be replaced with "y"s and vice versa. But the
> > ordering of the various combinations does not matter, and each line
> > looks OK.
>
> Since x = A was replaced by x = B and y = B was replaced by y = A, I
> just converted all x = load A to x = load B. Similarly for y. I think
> we can do either this or as you suggested replacing x's with y's.
Fair enough. The other thing that confused me was the "STORE B=4,"
showing up early in your replacement.
Thanx, Paul
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] doc: memory-barriers.txt: Correct example for reorderings
2014-08-28 21:39 ` Paul E. McKenney
@ 2014-08-28 21:45 ` Pranith Kumar
2014-09-02 16:08 ` Paul E. McKenney
0 siblings, 1 reply; 6+ messages in thread
From: Pranith Kumar @ 2014-08-28 21:45 UTC (permalink / raw)
To: Paul McKenney; +Cc: Randy Dunlap, open list:DOCUMENTATION, LKML
On Thu, Aug 28, 2014 at 5:39 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> On Thu, Aug 28, 2014 at 05:15:50PM -0400, Pranith Kumar wrote:
>> On Thu, Aug 28, 2014 at 5:00 PM, Paul E. McKenney
>> <paulmck@linux.vnet.ibm.com> wrote:
>> >
>> > I am really confused by the ordering of the new lines, as I would have
>> > expected the "x"s to be replaced with "y"s and vice versa. But the
>> > ordering of the various combinations does not matter, and each line
>> > looks OK.
>>
>> Since x = A was replaced by x = B and y = B was replaced by y = A, I
>> just converted all x = load A to x = load B. Similarly for y. I think
>> we can do either this or as you suggested replacing x's with y's.
>
> Fair enough. The other thing that confused me was the "STORE B=4,"
> showing up early in your replacement.
>
So I converted
STORE A=3, x=LOAD A->3
to
STORE B=4, x=LOAD B->4
since the later load into x wanted an updated value of B and not the
default. That is the reason you see STORE B = 4 in place of STORE A =
3
--
Pranith
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] doc: memory-barriers.txt: Correct example for reorderings
2014-08-28 21:45 ` Pranith Kumar
@ 2014-09-02 16:08 ` Paul E. McKenney
2014-09-03 3:30 ` Pranith Kumar
0 siblings, 1 reply; 6+ messages in thread
From: Paul E. McKenney @ 2014-09-02 16:08 UTC (permalink / raw)
To: Pranith Kumar; +Cc: Randy Dunlap, open list:DOCUMENTATION, LKML
On Thu, Aug 28, 2014 at 05:45:10PM -0400, Pranith Kumar wrote:
> On Thu, Aug 28, 2014 at 5:39 PM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > On Thu, Aug 28, 2014 at 05:15:50PM -0400, Pranith Kumar wrote:
> >> On Thu, Aug 28, 2014 at 5:00 PM, Paul E. McKenney
> >> <paulmck@linux.vnet.ibm.com> wrote:
> >> >
> >> > I am really confused by the ordering of the new lines, as I would have
> >> > expected the "x"s to be replaced with "y"s and vice versa. But the
> >> > ordering of the various combinations does not matter, and each line
> >> > looks OK.
> >>
> >> Since x = A was replaced by x = B and y = B was replaced by y = A, I
> >> just converted all x = load A to x = load B. Similarly for y. I think
> >> we can do either this or as you suggested replacing x's with y's.
> >
> > Fair enough. The other thing that confused me was the "STORE B=4,"
> > showing up early in your replacement.
>
> So I converted
>
> STORE A=3, x=LOAD A->3
>
> to
>
> STORE B=4, x=LOAD B->4
>
> since the later load into x wanted an updated value of B and not the
> default. That is the reason you see STORE B = 4 in place of STORE A =
> 3
Fair enough.
However, the list is supposed to be part of the full set of 24 possible
outcomes. Many readers would therefore expect the permutations to be
ordered in some way, so that the first column would have six of one thing,
six of the next thing, and so on, according to some pattern.
Could you please adjust in this way? Again, the point is to be the
first few items in a full set of permutations, not to illustrate selected
orderings/outcomes.
Thanx, Paul
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] doc: memory-barriers.txt: Correct example for reorderings
2014-09-02 16:08 ` Paul E. McKenney
@ 2014-09-03 3:30 ` Pranith Kumar
0 siblings, 0 replies; 6+ messages in thread
From: Pranith Kumar @ 2014-09-03 3:30 UTC (permalink / raw)
To: Paul McKenney; +Cc: Randy Dunlap, open list:DOCUMENTATION, LKML
On Tue, Sep 2, 2014 at 12:08 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> Could you please adjust in this way? Again, the point is to be the
> first few items in a full set of permutations, not to illustrate selected
> orderings/outcomes.
>
OK, if that is the case then replacing x with y is much easier. I will
send an updated patch. Thanks!
--
Pranith
^ permalink raw reply [flat|nested] 6+ messages in thread
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2014-08-25 13:08 [PATCH] doc: memory-barriers.txt: Correct example for reorderings Pranith Kumar
[not found] ` <53FF8B77.7000103@infradead.org>
[not found] ` <20140828210010.GM5001@linux.vnet.ibm.com>
2014-08-28 21:15 ` Pranith Kumar
2014-08-28 21:39 ` Paul E. McKenney
2014-08-28 21:45 ` Pranith Kumar
2014-09-02 16:08 ` Paul E. McKenney
2014-09-03 3:30 ` Pranith Kumar
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