svn commit: r184759 - user/kmacy/HEAD_fast_multi_xmit/sys/net
Attilio Rao
attilio at freebsd.org
Sat Nov 8 05:52:36 PST 2008
2008/11/8, Kip Macy <kmacy at freebsd.org>:
> Author: kmacy
> Date: Sat Nov 8 02:02:13 2008
> New Revision: 184759
> URL: http://svn.freebsd.org/changeset/base/184759
>
> Log:
> add memory barrier before critical_exit to ensure that all buffered updates are
> committed to main memory before a preemption is permitted
>
> Modified:
> user/kmacy/HEAD_fast_multi_xmit/sys/net/flowtable.c
>
> Modified: user/kmacy/HEAD_fast_multi_xmit/sys/net/flowtable.c
> ==============================================================================
> --- user/kmacy/HEAD_fast_multi_xmit/sys/net/flowtable.c Fri Nov 7 23:50:57 2008 (r184758)
> +++ user/kmacy/HEAD_fast_multi_xmit/sys/net/flowtable.c Sat Nov 8 02:02:13 2008 (r184759)
> @@ -35,6 +35,21 @@
> #define calloc(count, size) malloc((count)*(size), M_DEVBUF, M_WAITOK|M_ZERO)
>
>
> +
> +#if defined (__GNUC__)
> + #if #cpu(i386) || defined __i386 || defined i386 || defined __i386__ || #cpu(x86_64) || defined __x86_64__
> + #define mb() __asm__ __volatile__ ("sfence;": : :"memory")
> + #elif #cpu(sparc64) || defined sparc64 || defined __sparcv9
> + #define mb() __asm__ __volatile__ ("membar #MemIssue": : :"memory")
> + #elif #cpu(sparc) || defined sparc || defined __sparc__
> + #define mb() __asm__ __volatile__ ("stbar;": : :"memory")
> + #else
> + #define mb() /* XXX just to make this compile */
> + #endif
> +#else
> + #error "unknown compiler"
> +#endif
> +
> /*
> * Taken from http://burtleburtle.net/bob/c/lookup3.c
> */
> @@ -317,6 +332,7 @@ static void
> flowtable_pcpu_unlock(struct flowtable *table, uint32_t hash)
> {
>
> + mb();
> critical_exit();
> }
Definitively, I'm not sure we need this.
We alredy have memory barriers you could exploit which just require a
"dummy" object.
For example you could do:
flowtable_pcpu_unlock(struct flowtable *table, uint32_t hash)
{
(void)atomic_load_acq_ptr(&dummy);
...
--
Peace can only be achieved by understanding - A. Einstein
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