Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 4/7] ppc: open code cpu creation for machine types

[Greg Kurz <groug@kaod.org>]

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On Mon, 4 Jul 2016 08:32:04 +0200
Greg Kurz <groug@kaod.org> wrote:

> On Mon, 4 Jul 2016 13:54:55 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Sat, Jul 02, 2016 at 10:33:33AM +0200, Greg Kurz wrote:  
> > > On Sat, 2 Jul 2016 13:36:22 +0530
> > > Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:
> > >     
> > > > On Sat, Jul 02, 2016 at 12:41:48AM +0200, Greg Kurz wrote:    
> > > > > If we want to generate cpu_dt_id in the machine code, this must occur
> > > > > before the cpu gets realized. We must open code the cpu creation to be
> > > > > able to do this.
> > > > > 
> > > > > This patch just does that. It borrows some lines from previous work
> > > > > from Bharata to handle the feature parsing.
> > > > > 
> > > > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > > > ---
> > > > >  hw/ppc/ppc.c |   39 ++++++++++++++++++++++++++++++++++++++-
> > > > >  1 file changed, 38 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
> > > > > index dc3d214009c5..57f4ddd073d0 100644
> > > > > --- a/hw/ppc/ppc.c
> > > > > +++ b/hw/ppc/ppc.c
> > > > > @@ -32,6 +32,7 @@
> > > > >  #include "sysemu/cpus.h"
> > > > >  #include "hw/timer/m48t59.h"
> > > > >  #include "qemu/log.h"
> > > > > +#include "qapi/error.h"
> > > > >  #include "qemu/error-report.h"
> > > > >  #include "hw/loader.h"
> > > > >  #include "sysemu/kvm.h"
> > > > > @@ -1353,5 +1354,41 @@ PowerPCCPU *ppc_get_vcpu_by_dt_id(int cpu_dt_id)
> > > > > 
> > > > >  PowerPCCPU *ppc_cpu_init(const char *cpu_model)
> > > > >  {
> > > > > -    return POWERPC_CPU(cpu_generic_init(TYPE_POWERPC_CPU, cpu_model));
> > > > > +    PowerPCCPU *cpu;
> > > > > +    CPUClass *cc;
> > > > > +    ObjectClass *oc;
> > > > > +    gchar **model_pieces;
> > > > > +    Error *err = NULL;
> > > > > +
> > > > > +    model_pieces = g_strsplit(cpu_model, ",", 2);
> > > > > +    if (!model_pieces[0]) {
> > > > > +        error_report("Invalid/empty CPU model name");
> > > > > +        return NULL;
> > > > > +    }
> > > > > +
> > > > > +    oc = cpu_class_by_name(TYPE_POWERPC_CPU, model_pieces[0]);
> > > > > +    if (oc == NULL) {
> > > > > +        error_report("Unable to find CPU definition: %s", model_pieces[0]);
> > > > > +        return NULL;
> > > > > +    }
> > > > > +
> > > > > +    cpu = POWERPC_CPU(object_new(object_class_get_name(oc)));
> > > > > +
> > > > > +    cc = CPU_CLASS(oc);
> > > > > +    cc->parse_features(CPU(cpu), model_pieces[1], &err);      
> > > > 
> > > > Igor is working on a patchset to convert -cpu features into global properties.
> > > > IIUC, after that patchset, it is not recommended to parse the -cpu features
> > > > for every CPU but do it only once.
> > > >     
> > > 
> > > cpu_generic_init() in the current code also does the parsing, and as the title
> > > says, this patch is just about open coding the creation. I don't want to
> > > change behavior yet.
> > > 
> > > But yes, I agree that we should only parse features once and I'll be more than
> > > happy to fix this in a followup patch, based on Igor's work.
> > > 
> > > In the meantime, maybe I can add a comment stating that the parsing should go
> > > away ?    
> > 
> > Right.  But the thing is by open coding here, you're making two copies
> > that need to be fixed instead of one, which increases the chances of
> > error.
> > 
> > It seems like it would be safer to change the generic code so there's
> > a new generic function which doesn't do the realize which we can use
> > on ppc (and other platforms when/if they need it).
> > 
> > Doing the change just on ppc by making our own copy of
> > cpu_generic_init() seems more like to lead to future mistakes.
> >   
> 
> I had this in v1:
> 
> http://patchwork.ozlabs.org/patch/642216/
> 
> I'll repost it in v3.
> 

I tend to agree with Igor's latest feeback:

https://lists.nongnu.org/archive/html/qemu-devel/2016-07/msg00381.html

I'll keep the open coded version in v3.

> > > > That is what I attempted here in the context of supporting compat cpu type
> > > > for pseries-2.7:
> > > > 
> > > > https://www.mail-archive.com/qemu-devel@nongnu.org/msg381660.html
> > > >     
> > > 
> > > Yeah and this is where I borrowed some lines. :)
> > >     
> > > > Regards,
> > > > Bharata.
> > > >     
> > > 
> > > Cheers.
> > >     
> >   
> 


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