Am 23.06.2015 um 19:08 schrieb Eduardo Habkost: > On Tue, Jun 23, 2015 at 06:44:57PM +0200, Andreas Färber wrote: >> Am 23.06.2015 um 18:38 schrieb Eduardo Habkost: >>> On Tue, Jun 23, 2015 at 06:33:05PM +0200, Michael S. Tsirkin wrote: >>>> On Tue, Jun 23, 2015 at 05:25:55PM +0100, Daniel P. Berrange wrote: >>>>> Whether QEMU changed the CPU for existing machines, or only for new >>>>> machines is actually not the core problem. Even if we only changed >>>>> the CPU in new machines that would still be an unsatisfactory situation >>>>> because we want to be able to be able to access different versions of >>>>> the CPU without the machine type changing, and access different versions >>>>> of the machine type, without the CPU changing. IOW it is the fact that the >>>>> changes in CPU are tied to changes in machine type that is the core >>>>> problem. >>>> >>>> But that's because we are fixing bugs. If CPU X used to work on >>>> hardware Y in machine type A and stopped in machine type B, this is >>>> because we have determined that it's the right thing to do for the >>>> guests and the users. We don't break stuff just for fun. >>>> Why do you want to bring back the bugs we fixed? >>> >>> I didn't take the time to count them, but I bet most of the commits I >>> listed on my previous e-mail message are not bug fixes, but new >>> features. >> >> Huh? Of course the latest machine model get new features. The point is >> that the previous ones don't and that's what we are providing them for - >> libvirt is expected to choose one machine and the contract with QEMU is >> that for that machine the CPU does *not* grow new features, and we're >> going at great lengths to achieve that. So this thread feels more and >> more weird... > > We are not talking about changes to existing machines. We are talking > about having changes introduced in new machines (the one we did on > purpose) affecting the runnability of the VM.
You are talking abstract! Example 1: Point A: Machine pc-i440fx-2.3 exists Runs or runs not. Point B: Machine pc-i440fx-2.3 still exists Still runs or runs not due to guest ABI stability rules. Example 2: Point A: pc-i440fx-2.4 does not exist in 2.3 Does not run becomes it doesn't exist. Point B: New pc-i440fx-2.4 Runs or does not run, and if so has more features than pc-i440fx-2.3. There is no runnability problem - either it runs or it doesn't, but there's no change over time. This is what the machine -x.y versioning is all about. Andreas -- SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Felix Imendörffer, Jane Smithard, Dilip Upmanyu, Graham Norton; HRB 21284 (AG Nürnberg)
