Re: [PATCH 2/7] spapr, xive: Turn "nr-ends" property into "nr-servers" property

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Oct 04, 2019 at 08:51:19AM +0200, Greg Kurz wrote:
> On Fri, 4 Oct 2019 14:07:25 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Thu, Oct 03, 2019 at 02:01:13PM +0200, Greg Kurz wrote:
> > > The sPAPR XIVE object has an nr_ends field which happens to be a
> > > multiple of spapr_max_server_number(). It is currently set with
> > > the help of "nr-ends" property. This is a bit unfortunate since
> > > it exposes to the sPAPR irq frontend what should remain an
> > > implemantation detail within the XIVE backend.
> > > 
> > > It will be possible soon to inform the XIVE KVM device about the
> > > range of VCPU ids that may be used in the VM, as returned by the
> > > spapr_max_server_number() function. This will allow the device
> > > to substantially reduce the consumption of scarce resources
> > > in the XIVE HW.
> > > 
> > > For both reasons, replace the "nr-ends" property with an "nr-servers"
> > > one. The existing nr_ends field must be kept though since it tells how
> > > many ENDs are migrated, it is derived from "nr-servers" at realize time
> > > for simplicity. Convert spapr_dt_xive() to use it as well.
> > > 
> > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > ---
> > >  hw/intc/spapr_xive.c        |   21 ++++++++++++++++-----
> > >  hw/ppc/spapr_irq.c          |    2 +-
> > >  include/hw/ppc/spapr_xive.h |    1 +
> > >  3 files changed, 18 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
> > > index 04879abf2e7a..62888ddc68db 100644
> > > --- a/hw/intc/spapr_xive.c
> > > +++ b/hw/intc/spapr_xive.c
> > > @@ -99,6 +99,15 @@ int spapr_xive_end_to_target(uint8_t end_blk, uint32_t end_idx,
> > >      return 0;
> > >  }
> > >  
> > > +static uint32_t spapr_xive_vcpu_id_to_end_idx(uint32_t vcpu_id)
> > > +{
> > > +    /*
> > > +     * 8 XIVE END structures per CPU. One for each available
> > > +     * priority
> > > +     */
> > > +    return vcpu_id << 3;
> > > +}
> > > +
> > >  static void spapr_xive_cpu_to_end(PowerPCCPU *cpu, uint8_t prio,
> > >                                    uint8_t *out_end_blk, uint32_t *out_end_idx)
> > >  {
> > > @@ -109,7 +118,7 @@ static void spapr_xive_cpu_to_end(PowerPCCPU *cpu, uint8_t prio,
> > >      }
> > >  
> > >      if (out_end_idx) {
> > > -        *out_end_idx = (cpu->vcpu_id << 3) + prio;
> > > +        *out_end_idx = spapr_xive_vcpu_id_to_end_idx(cpu->vcpu_id) + prio;
> > >      }
> > >  }
> > >  
> > > @@ -283,11 +292,13 @@ static void spapr_xive_realize(DeviceState *dev, Error **errp)
> > >          return;
> > >      }
> > >  
> > > -    if (!xive->nr_ends) {
> > > -        error_setg(errp, "Number of interrupt needs to be greater 0");
> > > +    if (!xive->nr_servers) {
> > > +        error_setg(errp, "Number of interrupt servers must be greater than 0");
> > >          return;
> > >      }
> > >  
> > > +    xive->nr_ends = spapr_xive_vcpu_id_to_end_idx(xive->nr_servers);
> > 
> > I'd prefer not to store both nr_servers and nr_servers * 8 in the
> > structure.  I think you just want xive->nr_servers, then derive it any
> > any places that current look at xive->nr_ends.
> > 
> 
> Of course but unfortunately nr_ends is involved in migration:
> 
> static const VMStateDescription vmstate_spapr_xive = {
>     .name = TYPE_SPAPR_XIVE,
>     .version_id = 1,
>     .minimum_version_id = 1,
>     .pre_save = vmstate_spapr_xive_pre_save,
>     .post_load = NULL, /* handled at the machine level */
>     .fields = (VMStateField[]) {
>         VMSTATE_UINT32_EQUAL(nr_irqs, SpaprXive, NULL),
>         VMSTATE_STRUCT_VARRAY_POINTER_UINT32(eat, SpaprXive, nr_irqs,
>                                      vmstate_spapr_xive_eas, XiveEAS),
>         VMSTATE_STRUCT_VARRAY_POINTER_UINT32(endt, SpaprXive, nr_ends,
>                                                              ^^^^^^^^^^
>                                              vmstate_spapr_xive_end, XiveEND),
>         VMSTATE_END_OF_LIST()
>     },
> };
> 
> and we certainly cannot put nr_servers << 3 here. I suppose I should
> emphasize that even more in the changelog.

Ah, dangit, I forgot about that, though I've hit the same problem
before.  I'm actually less concerned about a comment in the changelog,
than in on the definition in the structure itself.

> We could possibly rename nr_ends to mig_nr_ends, and possibly only
> compute at migration time, but it doesn't buy much IMHO.

No, indeed not.

> > >      /*
> > >       * Initialize the internal sources, for IPIs and virtual devices.
> > >       */
> > > @@ -489,7 +500,7 @@ static const VMStateDescription vmstate_spapr_xive = {
> > >  
> > >  static Property spapr_xive_properties[] = {
> > >      DEFINE_PROP_UINT32("nr-irqs", SpaprXive, nr_irqs, 0),
> > > -    DEFINE_PROP_UINT32("nr-ends", SpaprXive, nr_ends, 0),
> > > +    DEFINE_PROP_UINT32("nr-servers", SpaprXive, nr_servers, 0),
> > 
> > Technically speaking the user can reach in using -global and modify
> > QOM properties like this, so this is arguably an interface breakage.
> 
> Drat, I didn't think about this one... :-\ but it seems that "spapr-xive"
> isn't user creatable and doesn't appear in the output of '-device help'.
> Not sure how -global behaves in this case...
> 
> > That said, I've always thought it was kind of a problem that the way
> > QOM is used internally thereby exposes as interface a bunch of things
> > that are really intended to be internal.
> > 
> 
> I tend to agree, nr-ends is really an internal detail that a typical
> sPAPR user should probably never see.
> 
> > So... I'm inclined to go ahead with this anyway.  I won't tell if you
> > don't.
> > 
> > >      DEFINE_PROP_UINT64("vc-base", SpaprXive, vc_base, SPAPR_XIVE_VC_BASE),
> > >      DEFINE_PROP_UINT64("tm-base", SpaprXive, tm_base, SPAPR_XIVE_TM_BASE),
> > >      DEFINE_PROP_END_OF_LIST(),
> > > @@ -1550,7 +1561,7 @@ void spapr_dt_xive(SpaprMachineState *spapr, uint32_t nr_servers, void *fdt,
> > >      /* Interrupt number ranges for the IPIs */
> > >      uint32_t lisn_ranges[] = {
> > >          cpu_to_be32(0),
> > > -        cpu_to_be32(nr_servers),
> > > +        cpu_to_be32(xive->nr_servers),
> > >      };
> > >      /*
> > >       * EQ size - the sizes of pages supported by the system 4K, 64K,
> > > diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
> > > index 457eabe24cda..025fd00143a2 100644
> > > --- a/hw/ppc/spapr_irq.c
> > > +++ b/hw/ppc/spapr_irq.c
> > > @@ -591,7 +591,7 @@ void spapr_irq_init(SpaprMachineState *spapr, Error **errp)
> > >           * 8 XIVE END structures per CPU. One for each available
> > >           * priority
> > >           */
> > > -        qdev_prop_set_uint32(dev, "nr-ends", nr_servers << 3);
> > > +        qdev_prop_set_uint32(dev, "nr-servers", nr_servers);
> > >          qdev_init_nofail(dev);
> > >  
> > >          spapr->xive = SPAPR_XIVE(dev);
> > > diff --git a/include/hw/ppc/spapr_xive.h b/include/hw/ppc/spapr_xive.h
> > > index 0df20a6590a5..4a4a6fc6be7f 100644
> > > --- a/include/hw/ppc/spapr_xive.h
> > > +++ b/include/hw/ppc/spapr_xive.h
> > > @@ -22,6 +22,7 @@ typedef struct SpaprXive {
> > >      /* Internal interrupt source for IPIs and virtual devices */
> > >      XiveSource    source;
> > >      hwaddr        vc_base;
> > > +    uint32_t      nr_servers;
> > 
> > This is a basic paraneter, not really related to the internal source
> > structure, so I'd move it up above that comment there.
> > 
> 
> Sure.
> 
> > >  
> > >      /* END ESB MMIOs */
> > >      XiveENDSource end_source;
> > > 
> > 
> 



-- 
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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