On Wed, Feb 24, 2016 at 02:41:17PM +0100, Igor Mammedov wrote: > On Wed, 24 Feb 2016 22:28:22 +1100 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > On Wed, Feb 24, 2016 at 11:48:33AM +0100, Igor Mammedov wrote: > > > On Wed, 24 Feb 2016 13:01:06 +1100 > > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > > > On Tue, Feb 23, 2016 at 12:18:59PM +0100, Igor Mammedov wrote: > > > > > On Tue, 23 Feb 2016 21:05:04 +1100 > > > > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > > > > > > > On Tue, Feb 23, 2016 at 03:10:26PM +0530, Bharata B Rao wrote: > > > > > > > On Tue, Feb 23, 2016 at 04:24:31PM +1100, David Gibson wrote: > > > > > > > > > > > > > > > Hi Andreas, > > > > > > > > > > > > > > > > I've now found (with Thomas' help) your RFC series for > > > > > > > > socket/core > > > > > > > > based cpu hotplug on x86 > > > > > > > > (https://github.com/afaerber/qemu-cpu/compare/qom-cpu-x86). It > > > > > > > > seems > > > > > > > > sensible enough as far as it goes, but doesn't seem to address > > > > > > > > a bunch > > > > > > > > of the things that I was attempting to do with the cpu-package > > > > > > > > proposal - and which we absolutely need for cpu hotplug on > > > > > > > > Power. > > > > > > > > > > > > > > > > 1) What interface do you envisage beyond cpu_add? > > > > > > > > > > > > > > > > The patches I see just construct extra socket and core objects, > > > > > > > > but > > > > > > > > still control hotplug (for x86) through the cpu_add interface. > > > > > > > > That > > > > > > > > interface is absolutely unusable on Power, since it operates on > > > > > > > > a > > > > > > > > per-thread basis, whereas the PAPR guest<->host interfaces can > > > > > > > > only > > > > > > > > communicate information at a per-core granularity. > > > > > > > > > > > > > > > > 2) When hotplugging at core or socket granularity, where would > > > > > > > > the > > > > > > > > code to construct the individual thread objects sit? > > > > > > > > > > > > > > > > Your series has the construction done in both the machine init > > > > > > > > path > > > > > > > > and the hotplug path. The latter works because hotplug occurs > > > > > > > > at > > > > > > > > thread granularity. If we're hotplugging at core or socket > > > > > > > > granularity what would do the construct? The core/socket object > > > > > > > > itself (in instance_init? in realize?); the hotplug handler? > > > > > > > > something else? > > > > > > > > > > > > > > > > 3) How does the management layer determine what is pluggable? > > > > > > > > > > > > > > > > Both the number of pluggable slots, and what it will need to do > > > > > > > > to > > > > > > > > populate them. > > > > > > > > > > > > > > > > 4) How do we enforce that toplogies illegal for the platform > > > > > > > > can't be > > > > > > > > constructed? > > > > > > > > > > > > > > 5) QOM-links > > > > > > > > > > > > > > Andreas, You have often talked about setting up links from > > > > > > > machine object > > > > > > > to the CPU objects. Would the below code correctly capture that > > > > > > > idea of > > > > > > > yours ? > > > > > > > > > > > > > > #define SPAPR_MACHINE_CPU_CORE_PROP "core" > > > > > > > > > > > > > > /* MachineClass.init for sPAPR */ > > > > > > > static void ppc_spapr_init(MachineState *machine) > > > > > > > { > > > > > > > sPAPRMachineState *spapr = SPAPR_MACHINE(machine); > > > > > > > int spapr_smp_cores = smp_cpus / smp_threads; > > > > > > > int spapr_max_cores = max_cpus / smp_threads; > > > > > > > > > > > > > > ... > > > > > > > for (i = 0; i < spapr_max_cores; i++) { > > > > > > > Object *obj = object_new(TYPE_SPAPR_CPU_CORE); > > > > > > > sPAPRCPUCore *core = SPAPR_CPU_CORE(obj); > > > > > > > char name[32]; > > > > > > > > > > > > > > snprintf(name, sizeof(name), "%s[%d]", > > > > > > > SPAPR_MACHINE_CPU_CORE_PROP, i); > > > > > > > > > > > > > > /* > > > > > > > * Create links from machine objects to all possible > > > > > > > cores. > > > > > > > */ > > > > > > > object_property_add_link(OBJECT(spapr), name, > > > > > > > TYPE_SPAPR_CPU_CORE, > > > > > > > (Object **)&spapr->core[i], > > > > > > > NULL, NULL, &error_abort); > > > > > > > > > > > > > > /* > > > > > > > * Set the QOM link from machine object to core object > > > > > > > for all > > > > > > > * boot time CPUs specified with -smp. For rest of the > > > > > > > hotpluggable > > > > > > > * cores this is done from the core hotplug path. > > > > > > > */ > > > > > > > if (i < spapr_smp_cores) { > > > > > > > object_property_set_link(OBJECT(spapr), OBJECT(core), > > > > > > > SPAPR_MACHINE_CPU_CORE_PROP, > > > > > > > &error_abort); > > > > > > > > > > > > I hope we can at least have a helper function to both construct the > > > > > > core and create the links, if we can't handle the link creation in > > > > > > the > > > > > > core object itself. > > > > > > > > > > > > Having to open-code it in each machine sounds like a recipe for > > > > > > subtle > > > > > > differences in presentation between platforms, which is exactly what > > > > > > we want to avoid. > > > > > Creating links doesn't give us much, it's just adds means for mgmt > > > > > to check how many CPUs could be hotplugged without keeping that > > > > > state in mgmt like it's now, so links are mostly useless if one > > > > > care where CPU is being plugged in. > > > > > The rest like enumerating exiting CPUs could be done by > > > > > traversing QOM tree, links would just simplify finding > > > > > CPUs putting them at fixed namespace. > > > > > > > > Simplifying finding CPUs is pretty much all we intended the links for. > > > Do mgmt really needs it? For machine it's easy to find CPUs under > > > /machine/[peripheral|unattached] by enumerating entries over there. > > > For human, one would need to implement a dedicated HMP command that > > > would do the same, so it doesn't really matter where links are > > > located. > > > > If we require management to go searching the whole device tree for > > cpus, I'm concerned they'll just assume they're in the x86 location > > instead, and we'll have to fix it over and over for every platform > > that puts them somewhere different. > CPUs are inherited from Device so inherited behaviour is that they > are pretty much at fixed location /machine/[peripheral|unattached] > regardless of platform QOM tree wise, like every other device.
Hmm.. that's true now, but I can see reasons you might want to put
CPUs on a different bus in future. In particular consider a machine
type modelling real hardware for a modern multisocket machine - these
are often built from several chips on a common fabric, each containing
several CPU cores, but also other peripherals and bus bridges.
--
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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