On Sat, Nov 22, 2008 at 05:55:56AM +0000, Kip Macy wrote: > Author: kmacy > Date: Sat Nov 22 05:55:56 2008 > New Revision: 185162 > URL: http://svn.freebsd.org/changeset/base/185162 > > Log: > - bump __FreeBSD version to reflect added buf_ring, memory barriers, > and ifnet functions > > - add memory barriers to <machine/atomic.h>
> Modified: head/sys/i386/include/atomic.h
> ==============================================================================
> --- head/sys/i386/include/atomic.h Sat Nov 22 01:48:20 2008
> (r185161)
> +++ head/sys/i386/include/atomic.h Sat Nov 22 05:55:56 2008
> (r185162)
> @@ -32,6 +32,21 @@
> #error this file needs sys/cdefs.h as a prerequisite
> #endif
>
> +
> +#if defined(I686_CPU)
> +#define mb() __asm__ __volatile__ ("mfence;": : :"memory")
> +#define wmb() __asm__ __volatile__ ("sfence;": : :"memory")
> +#define rmb() __asm__ __volatile__ ("lfence;": : :"memory")
> +#else
> +/*
> + * do we need a serializing instruction?
> + */
> +#define mb()
> +#define wmb()
> +#define rmb()
> +#endif
> +
> +
> /*
> * Various simple operations on memory, each of which is atomic in the
> * presence of interrupts and multiple processors.
AFAIR, sfence instruction was added with the Pentium III processor (SSE),
while lfence was introduced with the Pentium 4 (SSE2).
I think that #ifdef I686_CPU handling of the fences is wrong. We need to
use a serialized instruction on CPUs that does not support corresponding
fence, if needed.
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