On 09/28/2011 10:22 AM, Linus Torvalds wrote:
> On Wed, Sep 28, 2011 at 9:47 AM, Jeremy Fitzhardinge <jer...@goop.org> wrote:
>>
>> Could do something like:
>>
>> if (ticket->head >= 254)
>> prev = xadd(&ticket->head_tail, 0xff02);
>> else
>> prev = xadd(&ticket->head_tail, 0x0002);
>>
>> to compensate for the overflow.
>
> Oh wow. You havge an even more twisted mind than I do.
>
> I guess that will work, exactly because we control "head" and thus can
> know about the overflow in the low byte. But boy is that ugly ;)
>
> But at least you wouldn't need to do the loop with cmpxchg. So it's
> twisted and ugly, but migth be practical.
>
I suspect it should be coded as -254 in order to use a short immediate
if that is even possible...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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