Re: [Qemu-devel] [PATCH V3 01/11] atomic: introduce atomic operations

[Avi Kivity <avi@redhat.com>]

On 09/13/2012 11:19 AM, Paolo Bonzini wrote:
> Il 13/09/2012 10:14, Avi Kivity ha scritto:
>>>>> >>> +static inline void atomic_set(Atomic *v, int i)
>>>>> >>> +{
>>>>> >>> +    v->counter = i;
>>>>> >>> +}
>>>>> >>> +
>>>>> >>> +static inline int atomic_read(Atomic *v)
>>>>> >>> +{
>>>>> >>> +    return v->counter;
>>>>> >>> +}
>>>>> >>>
>>>> >>
>>>> >> So these two operations don't get mangled by the optimizer.
>>>> >>
>>> > Browsing linux code and reading lkml, find some similar material. But
>>> > they have moved volatile from ->counter to function - atomic_read().
>>> > As to atomic_read(), I think it need to prevent optimizer from
>>> > refetching issue, but as to atomic_set(), do we need ?
>> I think so, to prevent reordering.
> 
> Agreed.  Alternatively, stick a barrier() before and after the
> assignment and read.
> 
> But I don't really see the point in wrapping atomically-accessed
> variables in a struct.  

Preventing accidental naked access (to be reported in patch review as
"wardrobe malfunction").

> Are we going to add a variant for long, a
> variant for pointers, etc.?

template <typename T> ...;

> I already proposed my version of this at
> http://github.com/bonzini/qemu/commit/1b439343.

Atomic operations are sufficiently rare and sufficiently important to
warrant extra effort, so I prefer the explicitly typed variants.

-- 
error compiling committee.c: too many arguments to function