lkml.org 
[lkml]   [2013]   [Dec]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH tip/core/locking 4/4] Documentation/memory-barriers.txt: Document ACCESS_ONCE()

* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> + (*) The compiler is within its rights to reload a variable, for example,
> + in cases where high register pressure prevents the compiler from
> + keeping all data of interest in registers. The compiler might
> + therefore optimize the variable tmp out of our previous example:
> +
> + while (tmp = a)
> + do_something_with(tmp);
> +
> + This could result in the following code, which is perfectly safe in
> + single-threaded code, but can be fatal in concurrent code:
> +
> + while (a)
> + do_something_with(a);
> +
> + For example, the optimized version of this code could result in
> + passing a zero to do_something_with() in the case where the variable
> + a was modified by some other CPU between the "while" statement and
> + the call to do_something_with().

Nit: I guess references to variable names such as 'a' should be quoted
(same for 'tmp', 'b', etc):

For example, the optimized version of this code could result in
passing a zero to do_something_with() in the case where the variable
'a' was modified by some other CPU between the "while" statement and
the call to do_something_with().

which makes reading it less ambiguous and more fluid IMO. This
observation applies to the whole document as 'a' is used in many
places.

Thanks,

Ingo


\
 
 \ /
  Last update: 2013-12-05 11:01    [W:0.217 / U:0.268 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site