Am 09.09.2013 um 04:40 schrieb Alexey Kardashevskiy <a...@ozlabs.ru>:
> On 09/06/2013 01:11 AM, Alexander Graf wrote: >> >> On 05.09.2013, at 16:26, Benjamin Herrenschmidt wrote: >> >>> On Thu, 2013-09-05 at 16:14 +0200, Andreas Färber wrote: >>> >>>> Are you thinking of POWER8 having a different frequency than POWER8 in >>>> compat mode? Because migration from one -cpu to another is not supported >>>> elsewhere. >>>> >>>> Even if we want to migrate from one POWER7 revision to another, we >>>> should let the destination use the revision of the source (guest ABI!), >>>> via property if need be. Anything else will lead to confusion as to what >>>> is supported and what is not. That -cpu host is the default for >>>> convenience shouldn't relieve admins/libvirt to think about sensible >>>> setups like they have to on x86. >>> >>> Besides POWER8 uses 512Mhz too :-) It's been architected so it's >>> unlikely to change from now on. >> >> Ok, ditch the tb frequency then. We can always default to 512Mhz when it's >> absent. > > > QEMU uses what kvmppc_get_tbfreq() returns. And ppc_tb_t carries this > value. It does not use 512MHz automatically but migration should always > assume 512MHz :-/ > > If we remove it, I would like to add assert(tb_freq!=512MHz) into > timebase_pre_save() and timebase_post_load(), is that ok? Good point. This would break TCG migration, right? Alex > > > -- > Alexey