Why is wmb() a no-op on x86_64?

[Bryan O'Sullivan]

Hi, Andi -

I notice that wmb() is a no-op on x86_64 kernels unless
CONFIG_UNORDERED_IO is set.  Is there any particular reason for this?
It's not similarly conditional on other platforms, and as a consequence,
in our driver (which requires a write barrier in some situations for
correctness), I have to add the following piece of ugliness:

#if defined(CONFIG_X86_64) && !defined(CONFIG_UNORDERED_IO)
#define ipath_wmb() asm volatile("sfence" ::: "memory")
#else
#define ipath_wmb() wmb()
#endif

	<b

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