On Fri, Apr 07, 2017 at 10:15:07AM +0100, Will Deacon wrote:
> On Fri, Apr 07, 2017 at 02:37:36PM +0800, pierre Kuo wrote:
> > for below example, if MAX is defined to be 1, then the compiler knows (Q
> > % MAX) is equal to zero.
> > so compiler will transform the "else" part of code.
> >
> > q = READ_ONCE(a);
> > if (q % MAX) {
> > WRITE_ONCE(b, 1);
> > do_something();
> > } else {
> > WRITE_ONCE(b, 2);
> > do_something_else();
> > }
> >
> > So we modify the original document as below:
> >
> > q = READ_ONCE(a);
> > - WRITE_ONCE(b, 1);
> > + WRITE_ONCE(b, 2);
> > do_something_else();
> >
> > Signed-off-by: pierre Kuo <vichy.kuo@xxxxxxxxx>
> > ---
> > Documentation/memory-barriers.txt | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Yup, looks like a typo since the do_something_else() part is correct.
> Thanks for the fix:
>
> Acked-by: Will Deacon <will.deacon@xxxxxxx>
>
> I'm assuming somebody will pick this up.
I have queued it with you ack, thank you both!
Thanx, Paul
> Will
>
> > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
> > index d2b0a8d..08329cb 100644
> > --- a/Documentation/memory-barriers.txt
> > +++ b/Documentation/memory-barriers.txt
> > @@ -768,7 +768,7 @@ equal to zero, in which case the compiler is within its rights to
> > transform the above code into the following:
> >
> > q = READ_ONCE(a);
> > - WRITE_ONCE(b, 1);
> > + WRITE_ONCE(b, 2);
> > do_something_else();
> >
> > Given this transformation, the CPU is not required to respect the ordering
> > --
> > 1.9.1
> >
>
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