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

[Paolo Bonzini]

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.

Paolo