Re: [Qemu-devel] [Qemu-ppc] [PATCH v5 12/36] spapr: initialize VSMT before initializing the IRQ backend

[Greg Kurz <groug@kaod.org>]

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On Thu, 29 Nov 2018 12:02:48 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Nov 28, 2018 at 10:35:51AM +0100, Greg Kurz wrote:
> > On Wed, 28 Nov 2018 13:57:14 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >   
> > > On Fri, Nov 16, 2018 at 11:57:05AM +0100, Cédric Le Goater wrote:  
> > > > We will need to use xics_max_server_number() to create the sPAPRXive
> > > > object modeling the interrupt controller of the machine which is
> > > > created before the CPUs.
> > > > 
> > > > Signed-off-by: Cédric Le Goater <clg@kaod.org>    
> > > 
> > > My only concern here is that this moves the spapr_set_vsmt_mode()
> > > before some of the sanity checks in spapr_init_cpus().  Are we certain
> > > there are no edge cases that could cause badness?
> > >   
> > 
> > The early checks in spapr_init_cpus() filter out topologies that would
> > result in partially filled cores. They're only related to the rest of
> > the code that creates the boot CPUs. Before commit 1a5008fc17,
> > spapr_set_vsmt_mode() was even being called before spapr_init_cpus().
> > The rationale to move it there was to ensure it is called before the
> > first user of spapr->vsmt, which happens to be a call to
> > xics_max_server_number().  
> 
> Ok.
> 
> > Now that xics_max_server_number() needs to be called even earlier, I think a
> > better change is to have xics_max_server_number() to call spapr_set_vsmt_mode()
> > if spapr->vsmt isn't set.  
> 
> I'd rather not do that, but instead move it statically to where it
> needs to be.  That sort of lazy/on-demand initialization can result in
> really confusing behaviours depending on when a seemingly innocuous
> data-returning function is called, so I consider it a code smell.
> 

Fair enough, then:

Reviewed-by: Greg Kurz <groug@kaod.org>

> >   
> > > > ---
> > > >  hw/ppc/spapr.c | 10 +++++-----
> > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > > index 7afd1a175bf2..50cb9f9f4a02 100644
> > > > --- a/hw/ppc/spapr.c
> > > > +++ b/hw/ppc/spapr.c
> > > > @@ -2466,11 +2466,6 @@ static void spapr_init_cpus(sPAPRMachineState *spapr)
> > > >          boot_cores_nr = possible_cpus->len;
> > > >      }
> > > >  
> > > > -    /* VSMT must be set in order to be able to compute VCPU ids, ie to
> > > > -     * call xics_max_server_number() or spapr_vcpu_id().
> > > > -     */
> > > > -    spapr_set_vsmt_mode(spapr, &error_fatal);
> > > > -
> > > >      if (smc->pre_2_10_has_unused_icps) {
> > > >          int i;
> > > >  
> > > > @@ -2593,6 +2588,11 @@ static void spapr_machine_init(MachineState *machine)
> > > >      /* Setup a load limit for the ramdisk leaving room for SLOF and FDT */
> > > >      load_limit = MIN(spapr->rma_size, RTAS_MAX_ADDR) - FW_OVERHEAD;
> > > >  
> > > > +    /* VSMT must be set in order to be able to compute VCPU ids, ie to
> > > > +     * call xics_max_server_number() or spapr_vcpu_id().
> > > > +     */
> > > > +    spapr_set_vsmt_mode(spapr, &error_fatal);
> > > > +
> > > >      /* Set up Interrupt Controller before we create the VCPUs */
> > > >      smc->irq->init(spapr, &error_fatal);
> > > >      
> > >   
> >   
> 
> 
> 


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