David Gibson <da...@gibson.dropbear.id.au> writes: > On Fri, Feb 19, 2016 at 10:51:11AM +0100, Markus Armbruster wrote: >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> > On Thu, Feb 18, 2016 at 11:37:39AM +0100, Igor Mammedov wrote: >> >> On Thu, 18 Feb 2016 14:39:52 +1100 >> >> David Gibson <da...@gibson.dropbear.id.au> wrote: >> >> >> >> > On Tue, Feb 16, 2016 at 11:36:55AM +0100, Igor Mammedov wrote: >> >> > > On Mon, 15 Feb 2016 20:43:41 +0100 >> >> > > Markus Armbruster <arm...@redhat.com> wrote: >> >> > > >> >> > > > Igor Mammedov <imamm...@redhat.com> writes: >> >> > > > >> >> > > > > it will allow mgmt to query present and possible to hotplug CPUs >> >> > > > > it is required from a target platform that wish to support >> >> > > > > command to set board specific MachineClass.possible_cpus() hook, >> >> > > > > which will return a list of possible CPUs with options >> >> > > > > that would be needed for hotplugging possible CPUs. >> >> > > > > >> >> > > > > For RFC there are: >> >> > > > > 'arch_id': 'int' - mandatory unique CPU number, >> >> > > > > for x86 it's APIC ID for ARM it's MPIDR >> >> > > > > 'type': 'str' - CPU object type for usage with device_add >> >> > > > > >> >> > > > > and a set of optional fields that would allows mgmt tools >> >> > > > > to know at what granularity and where a new CPU could be >> >> > > > > hotplugged; >> >> > > > > [node],[socket],[core],[thread] >> >> > > > > Hopefully that should cover needs for CPU hotplug porposes for >> >> > > > > magor targets and we can extend structure in future adding >> >> > > > > more fields if it will be needed. >> >> > > > > >> >> > > > > also for present CPUs there is a 'cpu_link' field which >> >> > > > > would allow mgmt inspect whatever object/abstraction >> >> > > > > the target platform considers as CPU object. >> >> > > > > >> >> > > > > For RFC purposes implements only for x86 target so far. >> >> > > > >> >> > > > Adding ad hoc queries as we go won't scale. Could this be solved >> >> > > > by a >> >> > > > generic introspection interface? >> >> > > Do you mean generic QOM introspection? >> >> > > >> >> > > Using QOM we could have '/cpus' container and create QOM links >> >> > > for exiting (populated links) and possible (empty links) CPUs. >> >> > > However in that case link's name will need have a special format >> >> > > that will convey an information necessary for mgmt to hotplug >> >> > > a CPU object, at least: >> >> > > - where: [node],[socket],[core],[thread] options >> >> > > - optionally what CPU object to use with device_add command >> >> > >> >> > Hmm.. is it not enough to follow the link and get the topology >> >> > information by examining the target? >> >> One can't follow a link if it's an empty one, hence >> >> CPU placement information should be provided somehow, >> >> either: >> > >> > Ah, right, so the issue is determining the socket/core/thread >> > addresses that cpus which aren't yet present will have. >> > >> >> * by precreating cpu-package objects with properties that >> >> would describe it /could be inspected via OQM/ >> > >> > So, we could do this, but I think the natural way would be to have the >> > information for each potential thread in the package. Just putting >> > say "core number" in the package itself assumes more than I'd like >> > about how packages sit in the heirarchy. Plus, it means that >> > management has a bunch of cases to deal with: package has all the >> > information, package has just a core id, package has just a socket id, >> > and so forth. >> > >> > It is a but clunky that when the package is plugged, this information >> > will have to sit parallel to the array of actual thread links. >> > >> > Markus or Andreas is there a natural way to present a list of (node, >> > socket, core, thread) tuples in the package object? Preferably >> > without having to create a whole bunch of "potential thread" objects >> > just for the purpose. >> >> I'm just a dabbler when it comes to QOM, but I can try. >> >> I view a concrete cpu-package device (subtype of the abstract >> cpu-package device) as a composite device containing stuff like actual >> cores. > > So.. the idea is it's a bit more abstract than that. My intention is > that the package lists - in some manner - each of the threads > (i.e. vcpus) it contains / can contain. Depending on the platform it > *might* also have internal structure such as cores / sockets, but it > doesn't have to. Either way, the contained threads will be listed in > a common way, as a flat array. > >> To create a composite device, you start with the outer shell, then plug >> in components one by one. Components can be nested arbitrarily deep. >> >> Perhaps you can define the concrete cpu-package shell in a way that lets >> you query what you need to know from a mere shell (no components >> plugged). > > Right.. that's exactly what I'm suggesting, but I don't know enough > about the presentation of basic data in QOM to know quite how to > accomplish it. > >> >> or >> >> * via QMP/HMP command that would provide the same information >> >> only without need to precreate anything. The only difference >> >> is that it allows to use -device/device_add for new CPUs. >> > >> > I'd be ok with that option as well. I'd be thinking it would be >> > implemented via a class method on the package object which returns the >> > addresses that its contained threads will have, whether or not they're >> > present right now. Does that make sense? >> >> If you model CPU packages as composite cpu-package devices, then you >> should be able to plug and unplug these with device_add, unless plugging >> them requires complex wiring that can't be done in qdev / device_add, >> yet. > > There's a whole bunch of issues raised by allowing device_add of > cpus. Although they're certainly interesting and probably useful, I'd > really like to punt on them for the time being, so we can get some > sort of cpu hotplug working on Power (and s390 and others).
If you make it a device, you can still set cannot_instantiate_with_device_add_yet to disable -device / device_add for now, and unset it later, when you're ready for it. > The idea of the cpu packages is that - at least for now - the user > can't control their contents apart from the single "present" bit. > They already know what they can contain. Composite devices commonly do. They're not general containers. The "present" bit sounds like you propose to "pre-plug" all the possible CPU packages, and thus reduce CPU hot plug/unplug to enabling/disabling pre-plugged CPU packages. What if a board can take different kinds of CPU packages? Do we pre-plug all combinations? Then some combinations are non-sensical. How would we reject them? For instance, PC machines support a wide range of CPUs in various arrangements, but you generally need to use a single kind of CPU, and the kind of CPU restricts the possible arrangements. How would you model that? > There are a bunch of potential use cases this doesn't address, but I > think it *does* address a useful subset of currently interesting > cases, without precluding more flexible extensions in future. > >> If that's the case, a general solution for "device needs complex wiring" >> would be more useful than a one-off for CPU packages. >> >> [...] >>
