[PATCH v2] Documentation: rewrite confusing statement about memory barriers

[PATCH v2] Documentation: rewrite confusing statement about memory barriers

[Guilherme G. Piccoli]

In this specific portion of the write memory barriers description,
the documentation mentions sequential order of stores, which is
confusing since sequential ordering is not guaranteed.

This patch tries to improve the doc in order to avoid any
mis-understanding.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
---

v2: added Paul in CC.

 Documentation/memory-barriers.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index b759a60624fd..a4bbbd1b63a0 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -383,8 +383,8 @@ Memory barriers come in four basic varieties:
      to have any effect on loads.
 
      A CPU can be viewed as committing a sequence of store operations to the
-     memory system as time progresses.  All stores before a write barrier will
-     occur in the sequence _before_ all the stores after the write barrier.
+     memory system as time progresses.  All stores _before_ a write barrier
+     will occur _before_ all the stores after the write barrier.
 
      [!] Note that write barriers should normally be paired with read or data
      dependency barriers; see the "SMP barrier pairing" subsection.
-- 
2.14.1

Re: [PATCH v2] Documentation: rewrite confusing statement about memory barriers

[Paul E. McKenney]

On Thu, Sep 21, 2017 at 04:29:01PM -0300, Guilherme G. Piccoli wrote:
> In this specific portion of the write memory barriers description,
> the documentation mentions sequential order of stores, which is
> confusing since sequential ordering is not guaranteed.
> 
> This patch tries to improve the doc in order to avoid any
> mis-understanding.
> 
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>

Good catch, and you are quite correct, a write barrier orders only
before and after itself, doing nothing to impose order on preceding
writes among themselves.

Applied, thank you!

							Thanx, Paul

> ---
> 
> v2: added Paul in CC.
> 
>  Documentation/memory-barriers.txt | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> index b759a60624fd..a4bbbd1b63a0 100644
> --- a/Documentation/memory-barriers.txt
> +++ b/Documentation/memory-barriers.txt
> @@ -383,8 +383,8 @@ Memory barriers come in four basic varieties:
>       to have any effect on loads.
> 
>       A CPU can be viewed as committing a sequence of store operations to the
> -     memory system as time progresses.  All stores before a write barrier will
> -     occur in the sequence _before_ all the stores after the write barrier.
> +     memory system as time progresses.  All stores _before_ a write barrier
> +     will occur _before_ all the stores after the write barrier.
> 
>       [!] Note that write barriers should normally be paired with read or data
>       dependency barriers; see the "SMP barrier pairing" subsection.
> -- 
> 2.14.1
> 

Re: [PATCH v2] Documentation: rewrite confusing statement about memory barriers

[Guilherme G. Piccoli]

On 09/21/2017 04:50 PM, Paul E. McKenney wrote:
> On Thu, Sep 21, 2017 at 04:29:01PM -0300, Guilherme G. Piccoli wrote:
>> In this specific portion of the write memory barriers description,
>> the documentation mentions sequential order of stores, which is
>> confusing since sequential ordering is not guaranteed.
>>
>> This patch tries to improve the doc in order to avoid any
>> mis-understanding.
>>
>> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
> 
> Good catch, and you are quite correct, a write barrier orders only
> before and after itself, doing nothing to impose order on preceding
> writes among themselves.

That's nice, thanks a lot Paul! :)

> 
> Applied, thank you!
> 
> 							Thanx, Paul
> 
>> ---
>>
>> v2: added Paul in CC.
>>
>>  Documentation/memory-barriers.txt | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
>> index b759a60624fd..a4bbbd1b63a0 100644
>> --- a/Documentation/memory-barriers.txt
>> +++ b/Documentation/memory-barriers.txt
>> @@ -383,8 +383,8 @@ Memory barriers come in four basic varieties:
>>       to have any effect on loads.
>>
>>       A CPU can be viewed as committing a sequence of store operations to the
>> -     memory system as time progresses.  All stores before a write barrier will
>> -     occur in the sequence _before_ all the stores after the write barrier.
>> +     memory system as time progresses.  All stores _before_ a write barrier
>> +     will occur _before_ all the stores after the write barrier.
>>
>>       [!] Note that write barriers should normally be paired with read or data
>>       dependency barriers; see the "SMP barrier pairing" subsection.
>> -- 
>> 2.14.1
>>