Re: [Xen-devel] [PATCH 00/10] [PATCH RFC V2] Paravirtualized ticketlocks

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Wed, Sep 28, 2011 at 9:47 AM, Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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.

                   Linus

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