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[Xen-devel] Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C



On 08/06/2010 07:53 AM, Jeremy Fitzhardinge wrote:
On 08/06/2010 05:43 AM, Jan Beulich wrote:
You certainly mean "the compiler currently treats this as being:" - I
don't think there's a guarantee it'll always be doing so.

for (;;) {
if (inc.tickets.head == inc.tickets.tail)
goto out;
...
}
out: barrier();
}

(Which would probably be a reasonable way to clarify the code.)
I therefore think it needs to be written this way.

Agreed.


A call/return to an actual out-of-line function is a barrier (and will always be a barrier, as it is the fundamental ABI sequence points), but to an inline function it is not.

        -hpa

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