Re: [Xen-devel] [PATCH RFC 03/12] x86/ticketlock: Use C for __ticket_spin_unlock

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 07/20/2010 09:17 AM, Jeremy Fitzhardinge wrote:
> 
> "volatile" would be a compiler barrier, but it has no direct effect on,
> or relevence to, the CPU.  It just cares about the LOCK_PREFIX.  The
> "memory" clobber is probably unnecessary as well, since the constraints
> already tell the compiler the most important information.  We can add
> barriers separately as needed.
> 

You absolutely need volatile, since otherwise you're permitting the
compiler to split, re-execute or even drop the code.  Anything else
might work, by accident, but it's not clean.

        -hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.


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