On 13/03/2015 09:32, Paolo Bonzini wrote:
>
>
> On 13/03/2015 09:16, Fam Zheng wrote:
>>>>>> + if (atomic_cmpxchg(&bounce.in_use, false, true)) {
>>>>
>>>> atomic_or is enough...
>> atomic_cmpxchg is here to take the ownership of bounce iff it is not in use,
>> so
>> I think it is necessary.
>
> It's changing false to true and true to true, so you can do
>
> if (atomic_or(&bounce.in_use, 1)) {
> // was true already
> }
... and actually, atomic_xchg is even better (on x86, atomic_or is
compiled into a cmpxchg loop, but atomic_xchg is a single instruction).
Paolo
