lkml.org 
[lkml]   [2007]   [Aug]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subject[PATCH 0/24] make atomic_read() behave consistently across all architectures
As recent discussions[1], and bugs[2] have shown, there is a great deal of
confusion about the expected behavior of atomic_read(), compounded by the
fact that it is not the same on all architectures. Since users expect calls
to atomic_read() to actually perform a read, it is not desirable to allow
the compiler to optimize this away. Requiring the use of barrier() in this
case is inefficient, since we only want to re-load the atomic_t variable,
not everything else in scope.

This patchset makes the behavior of atomic_read uniform by removing the
volatile keyword from all atomic_t and atomic64_t definitions that currently
have it, and instead explicitly casts the variable as volatile in
atomic_read(). This leaves little room for creative optimization by the
compiler, and is in keeping with the principles behind "volatile considered
harmful".

Busy-waiters should still use cpu_relax(), but fast paths may be able to
reduce their use of barrier() between some atomic_read() calls.

-- Chris

1) http://lkml.org/lkml/2007/7/1/52
2) http://lkml.org/lkml/2007/8/8/122
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-08-09 15:17    [W:0.426 / U:2.808 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site