On Tue, Dec 02, 2014 at 04:15:19PM -0500, Jonathan Corbet wrote:
> On Thu, 27 Nov 2014 12:19:26 +0530
> Srikanth Thokala <sriku.linux@xxxxxxxxx> wrote:
>
> > Hi,
> >
> > Kindly review the patch.
>
> To me it looks right. Something like this, though, needs an ack from
> Paul (cc'd) before I can be really confident. Paul...?
I am guessing that this patch is against an old version of this file
(there have been two patches applied to this example in the last six
months). I believe that the current version is correct, in other words,
that Alexey Dobriyan and Pranith Kumar beat you to this one. ;-)
Please see below for the current version, which is in -tip as of
November 20th.
Thanx, Paul
> jon
>
> > Thanks
> > Srikanth
> >
> > On Tue, Nov 18, 2014 at 10:09 AM, Srikanth Thokala
> > <sriku.linux@xxxxxxxxx> wrote:
> > > In the first example, the loads into 'x' and 'y' on CPU 2 doesn't
> > > match the sequence of events described below it. To match the
> > > sequence of events, the values of 'A' and 'B' should be loaded
> > > into 'x' and 'y' respectively.
> > >
> > > Signed-off-by: Srikanth Thokala <sriku.linux@xxxxxxxxx>
> > > ---
> > > 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 22a969c..2770bce 100644
> > > --- a/Documentation/memory-barriers.txt
> > > +++ b/Documentation/memory-barriers.txt
> > > @@ -115,8 +115,8 @@ For example, consider the following sequence of events:
> > > CPU 1 CPU 2
> > > =============== ===============
> > > { A == 1; B == 2 }
> > > - A = 3; x = B;
> > > - B = 4; y = A;
> > > + A = 3; x = A;
> > > + B = 4; y = B;
> > >
> > > The set of accesses as seen by the memory system in the middle can be arranged
> > > in 24 different combinations:
For example, consider the following sequence of events:
CPU 1 CPU 2
=============== ===============
{ A == 1; B == 2 }
A = 3; x = B;
B = 4; y = A;
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, y=LOAD A->3, x=LOAD B->4
STORE A=3, STORE B=4, x=LOAD B->4, y=LOAD A->3
STORE A=3, y=LOAD A->3, STORE B=4, x=LOAD B->4
STORE A=3, y=LOAD A->3, x=LOAD B->2, STORE B=4
STORE A=3, x=LOAD B->2, STORE B=4, y=LOAD A->3
STORE A=3, x=LOAD B->2, y=LOAD A->3, STORE B=4
STORE B=4, STORE A=3, y=LOAD A->3, x=LOAD B->4
STORE B=4, ...
...
and can thus result in four different combinations of values:
x == 2, y == 1
x == 2, y == 3
x == 4, y == 1
x == 4, y == 3
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