On Tue, 13 Aug 2024, Edgar E. Iglesias wrote: > On Mon, Aug 12, 2024 at 06:47:17PM -0700, Stefano Stabellini wrote: > > On Mon, 12 Aug 2024, Edgar E. Iglesias wrote: > > > From: "Edgar E. Iglesias" <edgar.igles...@amd.com> > > > > > > Add SMP support for Xen PVH ARM guests. Create max_cpus ioreq > > > servers to handle hotplug. > > > > > > Signed-off-by: Edgar E. Iglesias <edgar.igles...@amd.com> > > > --- > > > hw/arm/xen_arm.c | 5 +++-- > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > diff --git a/hw/arm/xen_arm.c b/hw/arm/xen_arm.c > > > index 5f75cc3779..ef8315969c 100644 > > > --- a/hw/arm/xen_arm.c > > > +++ b/hw/arm/xen_arm.c > > > @@ -173,7 +173,7 @@ static void xen_arm_init(MachineState *machine) > > > > > > xen_init_ram(machine); > > > > > > - xen_register_ioreq(xam->state, machine->smp.cpus, > > > &xen_memory_listener); > > > + xen_register_ioreq(xam->state, machine->smp.max_cpus, > > > &xen_memory_listener); > > > > > > xen_create_virtio_mmio_devices(xam); > > > > > > @@ -218,7 +218,8 @@ static void xen_arm_machine_class_init(ObjectClass > > > *oc, void *data) > > > MachineClass *mc = MACHINE_CLASS(oc); > > > mc->desc = "Xen PVH ARM machine"; > > > mc->init = xen_arm_init; > > > - mc->max_cpus = 1; > > > + /* MAX number of vcpus supported by Xen. */ > > > + mc->max_cpus = GUEST_MAX_VCPUS; > > > > Will this cause allocations of data structures with 128 elements? > > Looking at hw/xen/xen-hvm-common.c:xen_do_ioreq_register it seems > > possible? Or hw/xen/xen-hvm-common.c:xen_do_ioreq_register is called > > Yes, in theory there's probably overhead with this but as you correctly > noted below, a PVH aware xl will set the max_cpus option to a lower value. > > With a non-pvh aware xl, I was a little worried about the overhead > but I couldn't see any visible slow-down on ARM neither in boot or in network > performance (I didn't run very sophisticated benchmarks). What do you mean by "non-pvh aware xl"? All useful versions of xl support pvh?
> > later on with the precise vCPU value which should be provided to QEMU > > via the -smp command line option > > (tools/libs/light/libxl_dm.c:libxl__build_device_model_args_new)? > > Yes, a pvh aware xl will for example pass -smp 2,maxcpus=4 based on > values from the xl.cfg. If the user doesn't set maxvcpus in xl.cfg, xl > will set maxvcpus to the same value as vcpus. OK good. In that case if this is just an initial value meant to be overwritten, I think it is best to keep it as 1.
