Re: [PATCH v3 10/10] perf/x86/rapl: Add per-core energy counter support for AMD CPUs

["Zhang, Rui" <rui.zhang@intel.com>]

Hi, Dhananjay
> 
> > 
> > [...]
> > 
> > > @@ -685,6 +774,13 @@ static void __init rapl_advertise(void)
> > >                                 rapl_pkg_domain_names[i],
> > > rapl_hw_unit[i]);
> > >                 }
> > >         }
> > > +
> > > +       for (i = 0; i < NR_RAPL_CORE_DOMAINS; i++) {
> > > +               if (rapl_core_cntr_mask & (1 << i)) {
> > > +                       pr_info("hw unit of domain %s 2^-%d
> > > Joules\n",
> > > +                               rapl_core_domain_names[i],
> > > rapl_hw_unit[i]);
> > 
> > rapl_hw_unit[] is for package pmu only and
> > rapl_hw_unit[0] is rapl_hw_unit[PERF_RAPL_PP0] rather than
> > rapl_hw_unit[PERF_RAPL_PER_CORE]
> > 
> > you cannot use rapl_hw_unit[i] to represent per-core rapl domain
> > unit.
> 
> Yes right, I saw that all the elements in the rapl_hw_unit array were
> actually 
> using the value from the same register "MSR_RAPL_POWER_UNIT" or
> "MSR_AMD_RAPL_POWER_UNIT".
> Except for the two quirks,
>  
>  737         case
> RAPL_UNIT_QUIRK_INTEL_HSW:                                           
>                                                                      
>                                                       
>  738                 rapl_hw_unit[PERF_RAPL_RAM] =
> 16;                                                                  
>                                                                      
>                      
>  739                
> break;                                                               
>                                                                      
>                                                    
>  740         /* SPR uses a fixed energy unit for Psys domain. */
>  741         case RAPL_UNIT_QUIRK_INTEL_SPR:
>  742                 rapl_hw_unit[PERF_RAPL_PSYS] = 0;
>  743                 break;
> 
> So, as for AMD systems the rapl_hw_unit[] elements will always have
> the same value, I ended 
> up using the rapl_hw_unit[PERF_RAPL_PP0] for
> rapl_hw_unit[PERF_RAPL_PER_CORE], but I do realize
> it is quite hacky. So, better to do it cleanly and add a separate
> array/variable for the core events.
> 
yeah, that is much better.
> 

> > 
> > >  
> > >  static struct rapl_model model_amd_hygon = {
> > >         .pkg_events     = BIT(PERF_RAPL_PKG),
> > > +       .core_events    = BIT(PERF_RAPL_PER_CORE),
> > >         .msr_power_unit = MSR_AMD_RAPL_POWER_UNIT,
> > > -       .rapl_msrs      = amd_rapl_pkg_msrs,
> > > +       .rapl_pkg_msrs  = amd_rapl_pkg_msrs,
> > > +       .rapl_core_msrs = amd_rapl_core_msrs,
> > >  };
> > >  
> > >  static const struct x86_cpu_id rapl_model_match[] __initconst =
> > > {
> > > @@ -858,6 +957,11 @@ static int __init rapl_pmu_init(void)
> > >  {
> > >         const struct x86_cpu_id *id;
> > >         int ret;
> > > +       int nr_rapl_pmu = topology_max_packages() *
> > > topology_max_dies_per_package();
> > > +       int nr_cores = topology_max_packages() *
> > > topology_num_cores_per_package();
> > 
> > I'd suggest either using two variables nr_pkgs/nr_cores, or reuse
> > one
> > variable nr_rapl_pmu for both pkg pmu and per-core pmu.
> 
> I understand your point, but the problem with that is, there are
> actually three scopes needed here
> 
> Some Intel systems need a *die* scope for the rapl_pmus_pkg PMU
> Some Intel systems and all AMD systems need a *package* scope for the
> rapl_pmus_pkg PMU
> And AMD systems need a *core* scope for the rapl_pmus_per_core PMU
> 
> I think what we can do is three variables, nr_dies (for all Intel
> systems as before), 
> nr_pkgs(for AMD systems rapl_pmus_pkg PMU)

Not necessarily, we already uses rapl_pmus_pkg for intel systems,
right?

>  and nr_cores(for rapl_pmus_per_core PMU)
> 
> Sounds good?

what about just one variable "count" and reuse it for every cases?

> 
> > 
> > > +
> > > +       if (rapl_pmu_is_pkg_scope())
> > > +               nr_rapl_pmu = topology_max_packages();
> > >  
> > >         id = x86_match_cpu(rapl_model_match);
> > >         if (!id)
> > > @@ -865,17 +969,34 @@ static int __init rapl_pmu_init(void)
> > >  
> > >         rapl_model = (struct rapl_model *) id->driver_data;
> > >  
> > > -       rapl_pkg_cntr_mask = perf_msr_probe(rapl_model-
> > > >rapl_msrs,
> > > PERF_RAPL_PKG_EVENTS_MAX,
> > > +       rapl_pkg_cntr_mask = perf_msr_probe(rapl_model-
> > > > rapl_pkg_msrs, PERF_RAPL_PKG_EVENTS_MAX,
> > >                                         false, (void *)
> > > &rapl_model-
> > > > pkg_events);
> > >  
> > >         ret = rapl_check_hw_unit();
> > >         if (ret)
> > >                 return ret;
> > >  
> > > -       ret = init_rapl_pmus(&rapl_pmus_pkg);
> > > +       ret = init_rapl_pmus(&rapl_pmus_pkg, nr_rapl_pmu,
> > > rapl_attr_groups, rapl_attr_update);
> > >         if (ret)
> > >                 return ret;
> > >  
> > > +       if (rapl_model->core_events) {
> > > +               rapl_core_cntr_mask = perf_msr_probe(rapl_model-
> > > > rapl_core_msrs,
> > > +                                                   
> > > PERF_RAPL_CORE_EVENTS_MAX, false,
> > > +                                                    (void *)
> > > &rapl_model->core_events);
> > > +
> > > +               ret = init_rapl_pmus(&rapl_pmus_core, nr_cores,
> > > +                                    rapl_per_core_attr_groups,
> > > rapl_per_core_attr_update);
> > > +               if (ret) {
> > > +                       /*
> > > +                        * If initialization of per_core PMU
> > > fails,
> > > reset per_core
> > > +                        * flag, and continue with power PMU
> > > initialization.
> > > +                        */
> > > +                       pr_warn("Per-core PMU initialization
> > > failed
> > > (%d)\n", ret);
> > > +                       rapl_model->core_events = 0UL;
> > > +               }
> > > +       }
> > > +
> > >         /*
> > >          * Install callbacks. Core will call them for each online
> > > cpu.
> > >          */
> > > @@ -889,6 +1010,20 @@ static int __init rapl_pmu_init(void)
> > >         if (ret)
> > >                 goto out1;
> > >  
> > > +       if (rapl_model->core_events) {
> > > +               ret = perf_pmu_register(&rapl_pmus_core->pmu,
> > > "power_per_core", -1);
> > > +               if (ret) {
> > > +                       /*
> > > +                        * If registration of per_core PMU fails,
> > > cleanup per_core PMU
> > > +                        * variables, reset the per_core flag and
> > > keep the
> > > +                        * power PMU untouched.
> > > +                        */
> > > +                       pr_warn("Per-core PMU registration failed
> > > (%d)\n", ret);
> > > +                       cleanup_rapl_pmus(rapl_pmus_core);
> > > +                       rapl_model->core_events = 0UL;
> > > +               }
> > > +       }
> > > +
> > >         rapl_advertise();
> > >         return 0;
> > >  
> > > @@ -906,5 +1041,9 @@ static void __exit intel_rapl_exit(void)
> > >         cpuhp_remove_state_nocalls(CPUHP_AP_PERF_X86_RAPL_ONLINE)
> > > ;
> > >         perf_pmu_unregister(&rapl_pmus_pkg->pmu);
> > >         cleanup_rapl_pmus(rapl_pmus_pkg);
> > > +       if (rapl_model->core_events) {
> > > +               perf_pmu_unregister(&rapl_pmus_core->pmu);
> > > +               cleanup_rapl_pmus(rapl_pmus_core);
> > > +       }
> > 
> > we do check rapl_pmus_core before accessing it, but we never check
> > rapl_pmus_pkg because the previous code assumes it always exists.
> > 
> > so could there be a problem if some one starts the per-core pmu
> > when
> > pkg pmu is unregistered and cleaned up?
> > 
> > say, in rapl_pmu_event_init(),
> > 
> > if (event->attr.type == rapl_pmus_pkg->pmu.type ||
> >    (rapl_pmus_core && event->attr.type == rapl_pmus_core-
> > >pmu.type))
> > 
> > this can break because rapl_pmus_pkg is freed, right?
> 
> Hmm, I think this situation can't arise as whenever the power PMU
> fails, we 
> directly go to the failure path and dont setup the per-core PMU(which
> means 
> no one will be able to start the per-core PMU), 
> Please let me know if there is a scenario where this assumption can
> fail.

I mean if we do module unload and access power-per-core pmu at the same
time, could there be a race?

why not just unregister and cleanup the per-core pmu before the pkg
pmu?
> 

thanks,
rui