On Fri, Sep 22, 2017 at 12:46:58PM +0200, Cédric Le Goater wrote: > On 09/22/2017 12:12 PM, David Gibson wrote: > > On Fri, Sep 22, 2017 at 08:07:06AM +0200, Cédric Le Goater wrote: > >> On 09/22/2017 08:00 AM, Nikunj A Dadhania wrote: > >>> David Gibson <da...@gibson.dropbear.id.au> writes: > >>> > >>>>>>> > >>>>>>> As smp_thread defaults to 1 in vl.c, similarly smp_cores also has the > >>>>>>> default value of 1 in vl.c. In powernv, we were setting nr-cores like > >>>>>>> this: > >>>>>>> > >>>>>>> object_property_set_int(chip, smp_cores, "nr-cores", > >>>>>>> &error_fatal); > >>>>>>> > >>>>>>> Even when there were multiple cpus (-smp 4), when the guest boots up, > >>>>>>> we > >>>>>>> just get one core (i.e. smp_cores was 1) with single > >>>>>>> thread(smp_threads > >>>>>>> was 1), which is wrong as per the command-line that was provided. > >>>>>> > >>>>>> Right, so, -smp 4 defaults to 4 sockets, each with 1 core of 1 > >>>>>> thread. If you can't supply 4 sockets you should error, but you > >>>>>> shouldn't go and change the number of cores per socket. > >>>>> > >>>>> OK, that makes sense now. And I do see that smp_cpus is 4 in the above > >>>>> case. Now looking more into it, i see that powernv has something called > >>>>> "num_chips", isnt this same as sockets ? Do we need num_chips > >>>>> separately? > >>>> > >>>> Ah, yes, I see. It's probably still reasonable to keep num_chips as > >>>> an internal variable, rather than using (smp_cpus / smp_cores / > >>>> smp_threads) everywhere. But we shouldn't have it as a direct > >>>> user-settable property, instead setting it from the -smp command line > >>>> option. > >>> > >>> Something like the below works till num_chips=2, after that guest does > >>> not boot up. This might be some limitation within the OS, Cedric might > >>> have some clue. > >> > >> Some controllers might need some more tweaking, PSI, LPC, to elect a > >> master one. > > > > Uh.. why? > > that's not true. I managed to boot a pnv machine with 4 chips/sockets > each having 4 cpus using a 4.4.9-openpower2 skiroot kernel, from an > openpower firmare 1.10 I think. Recent openpower kernel must be using > some new features/instructions that we don't manage well in QEMU. > > I would need to build a kernel with more output. > > >> Anyhow I don't think we want to deduce the number of chips > >> from the number of cpus. These two figures are very different. > > > > How so? It's not totally perfect, but making a single chip correspond > > to a "socket" in qemu's (somewhat x86 centric) terminology is still a > > pretty good match. > > well, it would be good to be able to define chips with different > numbers of cpus. That is something will we want to do for sure.
You mean multiple chips in a single system with non-uniform numbers of cores? Are there really such systems in the wild? -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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