Re: [Qemu-devel] [QEMU-PPC] [PATCH 1/2] ppc/spapr: Add implementation of hcall H_PURR

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

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On Mon, Jul 01, 2019 at 02:23:21PM +1000, Suraj Jitindar Singh wrote:
> On Fri, 2019-06-28 at 19:29 +1000, David Gibson wrote:
> > On Mon, Jun 24, 2019 at 03:58:11PM +1000, Suraj Jitindar Singh wrote:
> > > The hcall H_PURR is used by a guest to read the PURR (processor
> > > utilisation of resources register). A guest expects that this
> > > register
> > > will count at a rate of timebase scaled by the number of guest
> > > vcpus
> > > present in the vcore. That is the per vcpu purr will count at a
> > > rate of
> > > timebase / # vcpus per vcore.
> > > 
> > > Implement a handler for the H_PURR hcall and return the purr value
> > > divided by smp_threads so that the sum of the purr deltas across
> > > the
> > > vcpus of a vcore equals the timebase delta
> > > 
> > > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> > 
> > Does this need something new advertised in the hypertas DT entry?
> 
> Hi David,
> 
> There doesn't seem to be a concensus on what the return value from the
> H_PURR hcall should be, whether it just returns the hardware value or
> does some adjusting of the value based on guest smt mode as I've
> implemented in the patch below.

*eyeroll*.  Lack of forethought in PAPR strikes again.

> As such please drop this patch series.

Ok, will do.

> 
> The guest can just read the purr register directly anyway and then
> interpret the values as it pleases.
> 
> Kind Regards,
> Suraj
> 
> > 
> > > ---
> > >  hw/ppc/spapr_hcall.c | 24 ++++++++++++++++++++++++
> > >  1 file changed, 24 insertions(+)
> > > 
> > > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > > index aae9fd2b3e..88b3343f04 100644
> > > --- a/hw/ppc/spapr_hcall.c
> > > +++ b/hw/ppc/spapr_hcall.c
> > > @@ -1819,6 +1819,27 @@ static target_ulong h_update_dt(PowerPCCPU
> > > *cpu, SpaprMachineState *spapr,
> > >      return H_SUCCESS;
> > >  }
> > >  
> > > +static target_ulong h_purr(PowerPCCPU *cpu, SpaprMachineState
> > > *spapr,
> > > +                           target_ulong opcode, target_ulong
> > > *args)
> > > +{
> > > +    CPUPPCState *env = &cpu->env;
> > > +    target_ulong purr;
> > > +
> > > +    if (kvm_enabled()) {
> > > +        cpu_synchronize_state(CPU(cpu));
> > > +        /*
> > > +         * Divide by smp_threads so that the sum of the purr
> > > deltas across the
> > > +         * vcpus of a vcore equal the timebase delta.
> > > +         */
> > > +        purr = env->spr[SPR_PURR] / smp_threads;
> > > +    } else {
> > > +        purr = cpu_ppc_load_purr(env);
> > > +    }
> > > +    args[0] = purr;
> > > +
> > > +    return H_SUCCESS;
> > > +}
> > > +
> > >  static spapr_hcall_fn papr_hypercall_table[(MAX_HCALL_OPCODE / 4)
> > > + 1];
> > >  static spapr_hcall_fn kvmppc_hypercall_table[KVMPPC_HCALL_MAX -
> > > KVMPPC_HCALL_BASE + 1];
> > >  
> > > @@ -1915,6 +1936,9 @@ static void hypercall_register_types(void)
> > >      spapr_register_hypercall(H_LOGICAL_DCBF, h_logical_dcbf);
> > >      spapr_register_hypercall(KVMPPC_H_LOGICAL_MEMOP,
> > > h_logical_memop);
> > >  
> > > +    /* hcall-purr */
> > > +    spapr_register_hypercall(H_PURR, h_purr);
> > > +
> > >      /* qemu/KVM-PPC specific hcalls */
> > >      spapr_register_hypercall(KVMPPC_H_RTAS, h_rtas);
> > >  
> > 
> > 
> 

-- 
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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