On Tue, 14 May 2019 10:37:32 +0200 Christian Borntraeger <[email protected]> wrote:
> On 14.05.19 09:28, David Hildenbrand wrote: > >>>> But that can be tested using the runability information if I am not > >>>> wrong. > >>> > >>> You mean the cpu level information, right? > > > > Yes, query-cpu-definition includes for each model runability information > > via "unavailable-features" (valid under the started QEMU machine). > > > >>> > >>>> > >>>>> and others that we have today. > >>>>> > >>>>> So yes, I think this would be acceptable. > >>>> > >>>> I guess it is acceptable yes. I doubt anybody uses that many CPUs in > >>>> production either way. But you never know. > >>> > >>> I think that using that many cpus is a more uncommon setup, but I still > >>> think that having to wait for actual failure > >> > >> That can happen all the time today. You can easily say z14 in the xml when > >> on a zEC12. Only at startup you get the error. The question is really: > > > > "-smp 248 -cpu host" will no longer work, while e.g. "-smp 248 -cpu z12" > > will work. Actually, even "-smp 248" will no longer work on affected > > machines. > > > > That is why wonder if it is better to disable the feature and print a > > warning. Similar to CMMA, where want want to tolerate when CMMA is not > > possible in the current environment (huge pages). > > > > "Diag318 will not be enabled because it is not compatible with more than > > 240 CPUs". > > > > However, I still think that implementing support for more than one SCLP > > response page is the best solution. Guests will need adaptions for > 240 > > CPUs with Diag318, but who cares? Existing setups will continue to work. > > > > Implementing that SCLP thingy will avoid any warnings and any errors. It > > just works from the QEMU perspective. > > > > Is implementing this realistic? > > Yes it is but it will take time. I will try to get this rolling. To make > progress on the diag318 thing, can we error on startup now and simply > remove that check when when have implemented a larger sccb? If we would > now do all kinds of "change the max number games" would be harder to "fix". So, the idea right now is: - fail to start if you try to specify a diag318 device and more than 240 cpus (do we need a knob to turn off the device?) - in the future, support more than one SCLP response page I'm getting a bit lost in the discussion; but the above sounds reasonable to me.
