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SubjectRe: [PATCH v3 21/24] thermal: intel: hfi: Implement model-specific checks for task classification
On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
>
> In Alder Lake and Raptor Lake, the result of thread classification is more
> accurate when only one SMT sibling is busy. Classification results for
> class 2 and 3 are always reliable.
>
> To avoid unnecessary migrations, only update the class of a task if it has
> been the same during 4 consecutive user ticks.
>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Ionela Voinescu <ionela.voinescu@arm.com>
> Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Lukasz Luba <lukasz.luba@arm.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Tim C. Chen <tim.c.chen@intel.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: x86@kernel.org
> Cc: linux-pm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
> Changes since v2:
> * None
>
> 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.
> * Used the new names of the IPC classes members in task_struct.
> * Reworked helper functions to use sched_smt_siblings_idle() to query
> the idle state of the SMT siblings of a CPU.
> ---
> drivers/thermal/intel/intel_hfi.c | 60 ++++++++++++++++++++++++++++++-
> 1 file changed, 59 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> index 35d947f47550..fdb53e4cabc1 100644
> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -40,6 +40,7 @@
> #include <linux/workqueue.h>
>
> #include <asm/msr.h>
> +#include <asm/intel-family.h>
>
> #include "../thermal_core.h"
> #include "intel_hfi.h"
> @@ -209,9 +210,64 @@ static int __percpu *hfi_ipcc_scores;
> */
> #define HFI_UNCLASSIFIED_DEFAULT 1
>
> +#define CLASS_DEBOUNCER_SKIPS 4
> +
> +/**
> + * debounce_and_update_class() - Process and update a task's classification
> + *
> + * @p: The task of which the classification will be updated
> + * @new_ipcc: The new IPC classification
> + *
> + * Update the classification of @p with the new value that hardware provides.
> + * Only update the classification of @p if it has been the same during
> + * CLASS_DEBOUNCER_SKIPS consecutive ticks.
> + */
> +static void debounce_and_update_class(struct task_struct *p, u8 new_ipcc)
> +{
> + u16 debounce_skip;
> +
> + /* The class of @p changed. Only restart the debounce counter. */
> + if (p->ipcc_tmp != new_ipcc) {
> + p->ipcc_cntr = 1;
> + goto out;
> + }
> +
> + /*
> + * The class of @p did not change. Update it if it has been the same
> + * for CLASS_DEBOUNCER_SKIPS user ticks.
> + */
> + debounce_skip = p->ipcc_cntr + 1;
> + if (debounce_skip < CLASS_DEBOUNCER_SKIPS)
> + p->ipcc_cntr++;
> + else
> + p->ipcc = new_ipcc;
> +
> +out:
> + p->ipcc_tmp = new_ipcc;
> +}

Why does the code above belong to the Intel HFI driver? It doesn't
look like there is anything driver-specific in it.

> +
> +static bool classification_is_accurate(u8 hfi_class, bool smt_siblings_idle)
> +{
> + switch (boot_cpu_data.x86_model) {
> + case INTEL_FAM6_ALDERLAKE:
> + case INTEL_FAM6_ALDERLAKE_L:
> + case INTEL_FAM6_RAPTORLAKE:
> + case INTEL_FAM6_RAPTORLAKE_P:
> + case INTEL_FAM6_RAPTORLAKE_S:
> + if (hfi_class == 3 || hfi_class == 2 || smt_siblings_idle)
> + return true;
> +
> + return false;
> +
> + default:
> + return true;
> + }
> +}
> +
> void intel_hfi_update_ipcc(struct task_struct *curr)
> {
> union hfi_thread_feedback_char_msr msr;
> + bool idle;
>
> /* We should not be here if ITD is not supported. */
> if (!cpu_feature_enabled(X86_FEATURE_ITD)) {
> @@ -227,7 +283,9 @@ void intel_hfi_update_ipcc(struct task_struct *curr)
> * 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;
> + idle = sched_smt_siblings_idle(task_cpu(curr));
> + if (classification_is_accurate(msr.split.classid, idle))
> + debounce_and_update_class(curr, msr.split.classid + 1);
> }

I still think that this function should just return a number, possibly
including a special "no IPCC" value. It may be passed a bool argument
indicating whether or not the SMT siblings are idle.

>
> unsigned long intel_hfi_get_ipcc_score(unsigned short ipcc, int cpu)
> --

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