lkml.org 
[lkml]   [2002]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH] [RFC] [2.5 i386] GCC 3.1 -march support, PPRO_FENCE reduction, prefetch fixes and other CPU-related changes
    From
    Date
    On Mon, 2002-08-05 at 09:12, Luca Barbieri wrote:
    > So I'm only replacing the lock; addl $0,0(%%esp) with the Xfence
    > instructions which are more efficient.

    The original code has rmb not doing any kind of CPU operation, and wmb
    likewise. (Quoting 2.4 and 2.5.29 here)

    You don't need stronger barriers except on the Pentium Pro or the
    Winchip because of the guarantees already made by the processor and by
    the PCI interface.

    The only case you need a store fence with non buggy/weird processors is
    when you do non temporal stores. In that situation the barriers are
    still not needed because the non temporal using functions already have
    their own sfence instructions and need them.


    #define mb() __asm__ __volatile__ ("lock; addl $0,0(%%esp)":
    :"memory")
    #define rmb() mb()

    #ifdef CONFIG_X86_OOSTORE
    #define wmb() __asm__ __volatile__ ("lock; addl $0,0(%%esp)": :
    :"memory")
    #else
    #define wmb() __asm__ __volatile__ ("": : :"memory")
    #endif


    For the PPro a lock addl is the most efficient one I know of for working
    around the store order errata. If you want to optimise it further then
    the winchip appears to be fractionally faster using an rdmsr() but that
    impacts registers so wants more profiling



    -
    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: 2005-03-22 13:27    [W:3.178 / U:0.096 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site