Re: [Xen-devel] [PATCH] Cleanup rmb()/wmb() usage

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

Keir Fraser wrote:

> On 23 Feb 2005, at 03:38, Anthony Liguori wrote:
>
> asm/system.h is a private kernel header so should not be directly 
> included from user space. Inlcuding it may not work for all versions 
> of Linux, or for other architectures.
Actually, asm/system.h is designed for inclusion in userspace apps (and 
kernel space).  Hence the __KERNEL__ guards around certain sections.
It's used in a few notable userspace apps including glibc and MySQL.   
That said, Xen should not depend on Linux if it doesn't have to.
> We should probably merge the barrier defs we have scattered in the 
> tools directory into one low-level architectural header that we 
> include everywhere, and extend for x86/64, ia64, and so on.
Agreed.  Any ideas on where it would live?  I didn't see any likely 
place which is why I used asm/system.  io/ring.h seemed the closest fit 
but that's not architecture specific.
> Only Centaur clones that have been set up by the kernel to do write 
> combining. Xen does not ever enable write-combining on normal RAM and 
> so a barrier is never required.
Ah, that makes sense.  It still would be nice to have the barriers in a 
single location.  Pick a place and I'll submit a patch.
Regards,

--
Anthony Liguori
anthony@xxxxxxxxxxxxx



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