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:2.306 / U:0.172 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site