Re: [Qemu-devel] [PATCH 01/15] atomic: introduce atomic operations

[Avi Kivity]

On 08/08/2012 04:49 PM, Paolo Bonzini wrote:
> Il 08/08/2012 15:32, Peter Maydell ha scritto:
>>> > 1. GCC atomics look ugly, :) do not provide rmb/wmb, and in some
>>> > versions of GCC mb is known to be (wrongly) a no-op.
>>> >
>>> > 2. glib atomics do not provide mb/rmb/wmb either, and
>>> > g_atomic_int_get/g_atomic_int_set are inefficient: they add barriers
>>> > everywhere, while it is clearer if you put barriers manually, and you
>>> > often do not need barriers in the get side.  glib atomics also do not
>>> > provide xchg.
>> These are arguments in favour of "don't try to use atomic ops" --
>> if serious large projects like GCC and glib can't produce working
>> efficient implementations for all target architectures, what chance
>> do we have?
> 
> Well, maybe... but the flaws in both GCC and glib are small in size
> (even though large in importance, at least for us) and we can work
> around them easily.  mb/rmb/wmb is essentially the small set of atomic
> operations that we're already using.

We can easily define rmb()/wmb() to be __sync_synchronize() as a
default, and only override them where it matters.

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