On 17/7/26 15:55, Michael S. Tsirkin wrote:
On Fri, Jul 17, 2026 at 02:49:53PM +0100, Peter Maydell wrote:
On Fri, 17 Jul 2026 at 14:24, Michael S. Tsirkin <[email protected]> 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.
Note we have include/qemu/host-pci-mmio.h with s390x specific
optimizations in util/s390x_pci_mmio.c ...
