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? -- Alexey