Re: [PATCH v3 14/24] thermal: intel: hfi: Update the IPC class of the current task

[Ricardo Neri]

On Mon, Mar 27, 2023 at 06:42:28PM +0200, Rafael J. Wysocki wrote:
> On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
> <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote:
> >
> > Use Intel Thread Director classification to update the IPC class of a
> > task. Implement the arch_update_ipcc() interface of the scheduler.
> >
> > Cc: Ben Segall <bsegall@xxxxxxxxxx>
> > Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> > Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> > Cc: Ionela Voinescu <ionela.voinescu@xxxxxxx>
> > Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > Cc: Len Brown <len.brown@xxxxxxxxx>
> > Cc: Lukasz Luba <lukasz.luba@xxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxx>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
> > Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> > Cc: x86@xxxxxxxxxx
> > Cc: linux-pm@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> > ---
> > Changes since v2:
> >  * Removed the implementation of arch_has_ipc_classes().
> >
> > Changes since v1:
> >  * Adjusted the result the classification of Intel Thread Director to start
> >    at class 1. Class 0 for the scheduler means that the task is
> >    unclassified.
> >  * Redefined union hfi_thread_feedback_char_msr to ensure all
> >    bit-fields are packed. (PeterZ)
> >  * Removed CONFIG_INTEL_THREAD_DIRECTOR. (PeterZ)
> >  * Shortened the names of the functions that implement IPC classes.
> >  * Removed argument smt_siblings_idle from intel_hfi_update_ipcc().
> >    (PeterZ)
> > ---
> >  arch/x86/include/asm/topology.h   |  6 ++++++
> >  drivers/thermal/intel/intel_hfi.c | 32 +++++++++++++++++++++++++++++++
> >  2 files changed, 38 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> > index 458c891a8273..ffcdac3f398f 100644
> > --- a/arch/x86/include/asm/topology.h
> > +++ b/arch/x86/include/asm/topology.h
> > @@ -227,4 +227,10 @@ void init_freq_invariance_cppc(void);
> >  #define arch_init_invariance_cppc init_freq_invariance_cppc
> >  #endif
> >
> > +#if defined(CONFIG_IPC_CLASSES) && defined(CONFIG_INTEL_HFI_THERMAL)
> > +void intel_hfi_update_ipcc(struct task_struct *curr);
> > +
> > +#define arch_update_ipcc intel_hfi_update_ipcc
> > +#endif /* defined(CONFIG_IPC_CLASSES) && defined(CONFIG_INTEL_HFI_THERMAL) */
> > +
> >  #endif /* _ASM_X86_TOPOLOGY_H */
> > diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> > index b06021828892..530dcf57e06e 100644
> > --- a/drivers/thermal/intel/intel_hfi.c
> > +++ b/drivers/thermal/intel/intel_hfi.c
> > @@ -72,6 +72,17 @@ union cpuid6_edx {
> >         u32 full;
> >  };
> >
> > +#ifdef CONFIG_IPC_CLASSES
> > +union hfi_thread_feedback_char_msr {
> > +       struct {
> > +               u64     classid : 8;
> > +               u64     __reserved : 55;
> > +               u64     valid : 1;
> > +       } split;
> > +       u64 full;
> > +};
> > +#endif
> > +
> >  /**
> >   * struct hfi_cpu_data - HFI capabilities per CPU
> >   * @perf_cap:          Performance capability
> > @@ -174,6 +185,27 @@ static struct workqueue_struct *hfi_updates_wq;
> >  #ifdef CONFIG_IPC_CLASSES
> >  static int __percpu *hfi_ipcc_scores;
> >
> > +void intel_hfi_update_ipcc(struct task_struct *curr)
> > +{
> > +       union hfi_thread_feedback_char_msr msr;
> > +
> > +       /* We should not be here if ITD is not supported. */
> > +       if (!cpu_feature_enabled(X86_FEATURE_ITD)) {
> > +               pr_warn_once("task classification requested but not supported!");
> > +               return;
> > +       }
> > +
> > +       rdmsrl(MSR_IA32_HW_FEEDBACK_CHAR, msr.full);
> > +       if (!msr.split.valid)
> > +               return;
> > +
> > +       /*
> > +        * 0 is a valid classification for Intel Thread Director. A scheduler
> > +        * IPCC class of 0 means that the task is unclassified. Adjust.
> > +        */
> > +       curr->ipcc = msr.split.classid + 1;
> > +}
> 
> Wouldn't it be better to return the adjusted value from this function
> and let the caller store it where appropriate?
> 
> It doesn't look like it is necessary to pass the task_struct pointer to it.

Judging from this patch alone, yes, it does not make much sense to pass a
task_struct as argument. In patch 21, however, this function uses various
members of task_struct and makes it more convenient to have it as argument,
no?

> 
> > +
> >  static int alloc_hfi_ipcc_scores(void)
> >  {
> >         if (!cpu_feature_enabled(X86_FEATURE_ITD))
> > --