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

From: H. Peter Anvin
Date: Fri Aug 06 2010 - 13:52:55 EST

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.


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

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