On Mon, Mar 21, 2016 at 11:43:34AM +0100, Igor Mammedov wrote: > On Mon, 21 Mar 2016 14:57:53 +1100 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > On Fri, Mar 18, 2016 at 08:59:32AM +0530, Bharata B Rao wrote: > > > On Thu, Mar 17, 2016 at 09:03:43PM +1100, David Gibson wrote: > > > > On Wed, Mar 16, 2016 at 04:48:50PM +0100, Igor Mammedov wrote: > > > > > On Wed, 16 Mar 2016 09:18:03 +0530 > > > > > Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote: > > > > > > > > > > > On Mon, Mar 14, 2016 at 10:47:28AM +0100, Igor Mammedov wrote: > > > > > > > On Fri, 11 Mar 2016 10:24:29 +0530 > > > > > > > Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote: > > > > > > > > > > > > > > > Hi, > > > > > > > > > > > > > > > > This is the next version of "Core based CPU hotplug for PowerPC > > > > > > > > sPAPR" that > > > > > > > > was posted at > > > > > > > > https://lists.gnu.org/archive/html/qemu-ppc/2016-03/msg00081.html > > > > > > > > > > > > > > > > device_add semantics > > > > > > > > -------------------- > > > > > > > > For -smp 16,sockets=1,cores=2,threads=8,maxcpus=32 > > > > > > > > (qemu) device_add > > > > > > > > spapr-cpu-core,id=core2,core=16,cpu_model=host[,threads=8] > > > > > > > do you plan to allow user to hotplug different cpu_models? > > > > > > > If not it would be better to hide cpu_model from user > > > > > > > and set it from machine pre_plug handler. > > > > > > > > > > > > In my earlier implementations I derived cpu model from -cpu and > > > > > > threads from > > > > > > -smp,threads= commandline options and never exposed them to > > > > > > device_add > > > > > > command. > > > > > > > > > > > > Though we don't support heterogenous systems (different cpu models > > > > > > and/or > > > > > > threads) now, it was felt that it should be easy enough to support > > > > > > such > > > > > > systems if required in future, that's how cpu_model and threads > > > > > > became > > > > > > options for device_add. > > > > > > > > > > > > One of the things that David felt was missing from my earlier QMP > > > > > > query > > > > > > command (and which is true in your QMP query implementation also) > > > > > > is that > > > > > > we aren't exporting cpu_model at all, at least for not-yet-plugged > > > > > > cores. > > > > > > So should we include that or let management figure that out since it > > > > > > would already know about the CPU model. > > > > > 1. > > > > > so since you are not planning supporting heterogeneous setup yet, > > > > > I'd suggest to refrain from making user to provide cpu_model at > > > > > device_add time. Instead make machine code to set it for cores it > > > > > creates before core.realize() (yet another use for pre_plug()). > > > > > > > > > > That way mgmt doesn't have to figure out what cpu_model to set at > > > > > device_add time and doesn't have find out what property to use for > > > > > it. > > > > > > > > Yes.. of course you could also do the same thing for nr_threads, so > > > > I'm wondering whether there's a good argument to keep one in > > > > pre_plug() and one in query-hotpluggable-cpus. > > > > > > Right, so what should be the way forward ? Should we keep cpu_model= and > > > threads= options with device_add or just threads= or neither ? > > > > I'm inclined to keep them both in device_add - I like the idea of > > having an example on day 0 of advertising extra properties (beyond > > nr_threads and location) to set from query-hotpluggable-cpus. > > > > But, I'd probably change my mind if Igor or someone has a stronger > > opinion. > I don't have a strong opinion on this, but you have to keep in mind > that one you make it ABI you probably would have to maintain it forever. > > So far 'threads' and 'cpu_model' look like a constant values, > fixed at start-up time for every core. > Taking in account that user is not supposed to change them during > hotplug time and that they are the same for every core, > I'd go for conservative route and hide them in pre_plug() for now. > You always can expose them later if needed.
Hm, yes, I see your point. Hiding them in pre-plug does also make
life more convenient for someone (not libvirt) manually experimenting
with this - less to type on their device-add command.
> > If we advertise cpu_model, however, it should probably be changed to
> > cpu thread class name, since IIUC that's an existing advertised part
> > of the QOM interface, but cpu_model isn't.
> I still think that spapr-cpu-core should be an abstract type
> with a concrete set of derived cores types per each thread type.
> But this question is not related to hotplug, but rather to
> start-up of QEMU from scratch with -device and supported types
> discovery. So I'd postpone question for later and that's yet another
> reason why I'd like to hide cpu_model from user for now.
Ah.. yes, I think you're probably right, and we should have derived
types. It's a little bit awkward for spapr, but we can probably do
some macro magic to make it not too bad.
--
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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