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

[Peter Maydell]

On 8 August 2012 14:18, Paolo Bonzini <address@hidden> wrote:
> Il 08/08/2012 15:09, Stefan Hajnoczi ha scritto:
>> No need to roll our own or copy the implementation from the kernel.
>
> To some extent we need to because:
>
> 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?

-- PMM