Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH v1 05/10] cpu: Abstract CPU core type

[Igor Mammedov]

On Thu, 10 Mar 2016 16:04:29 +1100
David Gibson <address@hidden> wrote:

> On Wed, Mar 09, 2016 at 11:32:28AM +0100, Igor Mammedov wrote:
> > On Wed, 9 Mar 2016 13:55:51 +1100
> > David Gibson <address@hidden> wrote:
> >   
> > > On Tue, Mar 08, 2016 at 10:11:17AM +0100, Igor Mammedov wrote:  
> > > > On Tue, 8 Mar 2016 14:57:10 +1100
> > > > David Gibson <address@hidden> wrote:
> > > >     
> > > > > On Mon, Mar 07, 2016 at 11:40:11AM +0100, Igor Mammedov wrote:    
> > > > > > On Mon, 7 Mar 2016 14:01:55 +0530
> > > > > > Bharata B Rao <address@hidden> wrote:
> > > > > >       
> > > > > > > On Mon, Mar 07, 2016 at 02:36:55PM +1100, David Gibson wrote:     
> > > > > > >  
> > > > > > > > On Fri, Mar 04, 2016 at 07:07:20PM +0100, Igor Mammedov wrote:  
> > > > > > > >       
> > > > > > > > > On Fri, 4 Mar 2016 16:32:53 +0530
> > > > > > > > > Bharata B Rao <address@hidden> wrote:
> > > > > > > > >         
> > > > > > > > > > On Fri, Mar 04, 2016 at 11:38:45AM +0100, Igor Mammedov 
> > > > > > > > > > wrote:        
> > > > > > > > > > > On Fri,  4 Mar 2016 12:24:16 +0530
> > > > > > > > > > > Bharata B Rao <address@hidden> wrote:
> > > > > > > > > > >           
> > > > > > > > > > > > Add an abstract CPU core type that could be used by 
> > > > > > > > > > > > machines that want
> > > > > > > > > > > > to define and hotplug CPUs in core granularity.
> > > > > > > > > > > > 
> > > > > > > > > > > > Signed-off-by: Bharata B Rao <address@hidden>
> > > > > > > > > > > > ---
> > > > > > > > > > > >  hw/cpu/Makefile.objs  |  1 +
> > > > > > > > > > > >  hw/cpu/core.c         | 44 
> > > > > > > > > > > > ++++++++++++++++++++++++++++++++++++++++++++
> > > > > > > > > > > >  include/hw/cpu/core.h | 30 
> > > > > > > > > > > > ++++++++++++++++++++++++++++++
> > > > > > > > > > > >  3 files changed, 75 insertions(+)
> > > > > > > > > > > >  create mode 100644 hw/cpu/core.c
> > > > > > > > > > > >  create mode 100644 include/hw/cpu/core.h
> > > > > > > > > > > > 
> > > > > > > > > > > > diff --git a/hw/cpu/Makefile.objs b/hw/cpu/Makefile.objs
> > > > > > > > > > > > index 0954a18..942a4bb 100644
> > > > > > > > > > > > --- a/hw/cpu/Makefile.objs
> > > > > > > > > > > > +++ b/hw/cpu/Makefile.objs
> > > > > > > > > > > > @@ -2,4 +2,5 @@ obj-$(CONFIG_ARM11MPCORE) += 
> > > > > > > > > > > > arm11mpcore.o
> > > > > > > > > > > >  obj-$(CONFIG_REALVIEW) += realview_mpcore.o
> > > > > > > > > > > >  obj-$(CONFIG_A9MPCORE) += a9mpcore.o
> > > > > > > > > > > >  obj-$(CONFIG_A15MPCORE) += a15mpcore.o
> > > > > > > > > > > > +obj-y += core.o
> > > > > > > > > > > >  
> > > > > > > > > > > > diff --git a/hw/cpu/core.c b/hw/cpu/core.c
> > > > > > > > > > > > new file mode 100644
> > > > > > > > > > > > index 0000000..d8caf37
> > > > > > > > > > > > --- /dev/null
> > > > > > > > > > > > +++ b/hw/cpu/core.c
> > > > > > > > > > > > @@ -0,0 +1,44 @@
> > > > > > > > > > > > +/*
> > > > > > > > > > > > + * CPU core abstract device
> > > > > > > > > > > > + *
> > > > > > > > > > > > + * Copyright (C) 2016 Bharata B Rao <address@hidden>
> > > > > > > > > > > > + *
> > > > > > > > > > > > + * This work is licensed under the terms of the GNU 
> > > > > > > > > > > > GPL, version 2 or later.
> > > > > > > > > > > > + * See the COPYING file in the top-level directory.
> > > > > > > > > > > > + */
> > > > > > > > > > > > +#include "hw/cpu/core.h"
> > > > > > > > > > > > +
> > > > > > > > > > > > +static char *core_prop_get_slot(Object *obj, Error 
> > > > > > > > > > > > **errp)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +    CPUCore *core = CPU_CORE(obj);
> > > > > > > > > > > > +
> > > > > > > > > > > > +    return g_strdup(core->slot);
> > > > > > > > > > > > +}
> > > > > > > > > > > > +
> > > > > > > > > > > > +static void core_prop_set_slot(Object *obj, const char 
> > > > > > > > > > > > *val, Error **errp)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +    CPUCore *core = CPU_CORE(obj);
> > > > > > > > > > > > +
> > > > > > > > > > > > +    core->slot = g_strdup(val);
> > > > > > > > > > > > +}
> > > > > > > > > > > > +
> > > > > > > > > > > > +static void cpu_core_instance_init(Object *obj)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +    object_property_add_str(obj, "slot", 
> > > > > > > > > > > > core_prop_get_slot, core_prop_set_slot,
> > > > > > > > > > > > +                            NULL);
> > > > > > > > > > > > +}
> > > > > > > > > > > > +
> > > > > > > > > > > > +static const TypeInfo cpu_core_type_info = {
> > > > > > > > > > > > +    .name = TYPE_CPU_CORE,
> > > > > > > > > > > > +    .parent = TYPE_DEVICE,
> > > > > > > > > > > > +    .abstract = true,
> > > > > > > > > > > > +    .instance_size = sizeof(CPUCore),
> > > > > > > > > > > > +    .instance_init = cpu_core_instance_init,
> > > > > > > > > > > > +};
> > > > > > > > > > > > +
> > > > > > > > > > > > +static void cpu_core_register_types(void)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +    type_register_static(&cpu_core_type_info);
> > > > > > > > > > > > +}
> > > > > > > > > > > > +
> > > > > > > > > > > > +type_init(cpu_core_register_types)
> > > > > > > > > > > > diff --git a/include/hw/cpu/core.h 
> > > > > > > > > > > > b/include/hw/cpu/core.h
> > > > > > > > > > > > new file mode 100644
> > > > > > > > > > > > index 0000000..2daa724
> > > > > > > > > > > > --- /dev/null
> > > > > > > > > > > > +++ b/include/hw/cpu/core.h
> > > > > > > > > > > > @@ -0,0 +1,30 @@
> > > > > > > > > > > > +/*
> > > > > > > > > > > > + * CPU core abstract device
> > > > > > > > > > > > + *
> > > > > > > > > > > > + * Copyright (C) 2016 Bharata B Rao <address@hidden>
> > > > > > > > > > > > + *
> > > > > > > > > > > > + * This work is licensed under the terms of the GNU 
> > > > > > > > > > > > GPL, version 2 or later.
> > > > > > > > > > > > + * See the COPYING file in the top-level directory.
> > > > > > > > > > > > + */
> > > > > > > > > > > > +#ifndef HW_CPU_CORE_H
> > > > > > > > > > > > +#define HW_CPU_CORE_H
> > > > > > > > > > > > +
> > > > > > > > > > > > +#include "qemu/osdep.h"
> > > > > > > > > > > > +#include "hw/qdev.h"
> > > > > > > > > > > > +
> > > > > > > > > > > > +#define TYPE_CPU_CORE "cpu-core"
> > > > > > > > > > > > +
> > > > > > > > > > > > +#define CPU_CORE(obj) \
> > > > > > > > > > > > +    OBJECT_CHECK(CPUCore, (obj), TYPE_CPU_CORE)
> > > > > > > > > > > > +
> > > > > > > > > > > > +typedef struct CPUCore {
> > > > > > > > > > > > +    /*< private >*/
> > > > > > > > > > > > +    DeviceState parent_obj;
> > > > > > > > > > > > +
> > > > > > > > > > > > +    /*< public >*/
> > > > > > > > > > > > +    char *slot;
> > > > > > > > > > > > +} CPUCore;
> > > > > > > > > > > > +
> > > > > > > > > > > > +#define CPU_CORE_SLOT_PROP "slot"          
> > > > > > > > > > > as it's generic property I'd rename to 'core' so it would 
> > > > > > > > > > > fit all users          
> > > > > > > > > > 
> > > > > > > > > > Ok. Also note that this is a string property which is 
> > > > > > > > > > associated with the
> > > > > > > > > > link name (string) that we created from machine object to 
> > > > > > > > > > this core. I think
> > > > > > > > > > it would be ideal if this becomes an interger  property in 
> > > > > > > > > > which case it
> > > > > > > > > > becomes easier to feed the core location into your 
> > > > > > > > > > CPUSlotProperties.core.        
> > > > > > > > > agreed, it should be core number.        
> > > > > > > > 
> > > > > > > > The slot stuff is continuing to confuse me a bit.  I see that 
> > > > > > > > we need
> > > > > > > > some kind of "address" value, but how best to do it is not 
> > > > > > > > clear to
> > > > > > > > me.
> > > > > > > > 
> > > > > > > > Changing this to an integer sounds like it's probably a good 
> > > > > > > > idea.
> > > > > > > > I'm a bit wary of just calling it "core" though.  Do all 
> > > > > > > > platforms
> > > > > > > > even necessarily have a core id?
> > > > > > > > 
> > > > > > > > I'm wondering if the addressing is something that needs to move 
> > > > > > > > the
> > > > > > > > the platform specific subtypes, while some other stuff can move 
> > > > > > > > to the
> > > > > > > > generic base type.
> > > > > > > >         
> > > > > > > > > > > on top of that I'd add numeric 'threads' property to base 
> > > > > > > > > > > class so
> > > > > > > > > > > all derived cores would inherit it.
> > > > > > > > > > > 
> > > > > > > > > > > Then as easy integration with -smp threads=x, a machine 
> > > > > > > > > > > could push
> > > > > > > > > > > a global variable 'cpu-core.threads=[smp_threads]' which 
> > > > > > > > > > > would
> > > > > > > > > > > make every created cpu-core object to have threads set
> > > > > > > > > > > at instance_init() time (device_init).
> > > > > > > > > > > 
> > > > > > > > > > > That way user won't have to specify 'threads=y' for every
> > > > > > > > > > >   device_add spapr-core,core=x
> > > > > > > > > > > as it will be taken from global property 
> > > > > > > > > > > 'cpu-core.threads'
> > > > > > > > > > > but if user wishes he/she still could override global by 
> > > > > > > > > > > explicitly
> > > > > > > > > > > providing thread property at device_add time:
> > > > > > > > > > >   device_add spapr-core,core=x,threads=y
> > > > > > > > > > > 
> > > > > > > > > > > wrt this series it would mean, instead of creating 
> > > > > > > > > > > threads in property
> > > > > > > > > > > setter, delaying threads creation to core.realize() time,
> > > > > > > > > > > but since realize is allowed to fail it should be fine do 
> > > > > > > > > > > so.          
> > > > > > > > > > 
> > > > > > > > > > Ok that would suit us as there are two properties on which 
> > > > > > > > > > thread creation
> > > > > > > > > > is dependent upon: nr_threads and cpu_model. If thread 
> > > > > > > > > > objects can be
> > > > > > > > > > created at core realize time, then we don't have to resort 
> > > > > > > > > > to the ugliness
> > > > > > > > > > of creating the threads from either of the property 
> > > > > > > > > > setters. I always
> > > > > > > > > > assumed that we shouldn't be creating objects from realize, 
> > > > > > > > > > but if that
> > > > > > > > > > is fine, it is good.        
> > > > > > > > > since realize is allowed to fail, it should be safe from 
> > > > > > > > > hotplug pov
> > > > > > > > > to create internal objects there, as far as proper cleanups 
> > > > > > > > > are done
> > > > > > > > > for failure path.        
> > > > > > > > 
> > > > > > > > Right, moving the "nr_threads" property to the base type seems 
> > > > > > > > like a
> > > > > > > > good idea to me.        
> > > > > > > 
> > > > > > > And we will also move the cpu_model property (now being tracked by
> > > > > > > an ObjectClass pointer) to the base type ?      
> > > > > > I'm not sure that moving cpu_model to the base class is the right 
> > > > > > thing,
> > > > > > I'd keep it local to platform for now.      
> > > > > 
> > > > > I tend to agree, although I'm not sure that I could really explain why
> > > > > :/
> > > > >     
> > > > > > Could you have several spapr core types? One per CPU model?
> > > > > > That way you won't need to track cpu_model when using device_add.   
> > > > > >    
> > > > > 
> > > > > We could in theory, but it would be pretty inconvenient.  Because this
> > > > > is a paravirt platform, there really can't be any core-level
> > > > > difference between them, and it would mean creating a fair batch of
> > > > > core types for the various minor POWER7 and POWER8 variants - and
> > > > > needing to update this whenever IBM makes a new version.  I suspect it
> > > > > would also introduce more wrinkles in order to have a correct
> > > > > "spapr-core-host" type matching the "HOST" cpu thread type.  Since KVM
> > > > > (HV) only supports the HOST thread type, that's a fairly big issue.   
> > > > >  
> > > > Welcome to x86 world, that's roughly what we have there.    
> > > 
> > > I don't really follow you.  x86 doesn't have core devices at all for
> > > the moment.
> > > 
> > > What I'm saying here is that using different core subtypes for every
> > > cpu subtype on power would mean 2 types for each minor variant, rather
> > > than just 1.  
> > I think the same applies to cpu_model and transitioning CPUs to -device.
> > X86 also has a bunch of cpu_model-s which have some minor variations
> > but it still generates a type per cpu_model.
> > If some day we are to implement socket objects for x86 that would also
> > mean to have a socket types per each cpu model.  
> 
> Hmm.  I guess.
> 
> What concerns me is the possible combinatorial explosion of # cpu
> models * # of machine types leading to an enormous number of
> core/socket types.
>
> The other thing is that the platform specific core types belong with
> the machine type code, which means they can't naturally use macro
> magic or whatever to generate them in parallel with the thread device
> types in the core target-ppc code.
on x86 when introducing a new feature or changing behavior 
of existing cpu_model, cpu type stays the same but we amend some of
it's properties using compat machine infrastructure.
Though I'm not sure if it could help in SPAPR case.
 

> > As I understand cpu_model is a legacy option which should translate to
> > a corresponding QOM type (CPU device) which could be used with
> > -device/device_add.  
> 
> Sure, but the "cpu_model" parameter could be "thread type name" just
> as easily.
> 
> > As analogy, QEMU has legacy -net model=foo[1234] option, but when network 
> > cards
> > were converted to -device interface that in the end became a set of QOM 
> > types
> > like -device foo[1234], it was easier in case of network cards as
> > they where a separate devices models to begin with, the thing to note
> > here is that they weren't converted to a single 'network_card' type with
> > 'model' property.  
>