Re: [PATCH v3 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jul 17, 2026 at 02:49:53PM +0100, Peter Maydell wrote:
> On Fri, 17 Jul 2026 at 14:24, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Thu, Jul 09, 2026 at 07:52:12PM +1000, Gavin Shan wrote:
> > > Hi Michael and Peter,
> 
> > >
> > > Could you help to confirm if the conclusion is to have unified qemu_ram_{copy, move}()
> > > for all architectures? In qemu_ram_{copy, move}(), the fixed sized accesses like
> > > 1/2/4/8 bytes are handled by __builtin_{memcpy, memmove}() and fall back to
> > > memcpy/memmove() for other sized accesses. It's basically what was proposed by
> > > Michael :-)
> >
> > No. __builtin_ and  memcpy/memmove are same on modern linuxes.
> >
> > I'd say as a 1st step, on x86 hosts we can do a fixed size
> > memmove for 1/2/4/8, on other hosts
> > *aligned* 1/2/4/8 bytes can do
> >  __atomic_store ... __ATOMIC_RELAXED
> > and the rest can hobble along on memmove
> > and hope for the best.
> 
> I don't think we should be doing something that's x86-host specific,
> as I've mentioned previously.
> 
> -- PMM

Shrug. Of course we already have arch specific code in asm.
But we can make the unaligned 1/2/4/8 for x86 host a separate
optimization on top. They are unlikely to be common.

-- 
MST