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SubjectRe: [PATCH v3 13/24] thermal: intel: hfi: Store per-CPU IPCC scores
On Tue, Feb 7, 2023 at 6:02 AM Ricardo Neri
<ricardo.neri-calderon@linux.intel.com> wrote:
>
> The scheduler reads the IPCC scores when balancing load. These reads can
> be quite frequent. Hardware can also update the HFI table frequently.
> Concurrent access may cause a lot of lock contention. It gets worse as the
> number of CPUs increases.
>
> Instead, create separate per-CPU IPCC scores that the scheduler can read
> without the HFI table lock.
>
> 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
> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
> Changes since v2:
> * Only create these per-CPU variables when Intel Thread Director is
> supported.
>
> Changes since v1:
> * Added this patch.
> ---
> drivers/thermal/intel/intel_hfi.c | 46 +++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/drivers/thermal/intel/intel_hfi.c b/drivers/thermal/intel/intel_hfi.c
> index 2527ae3836c7..b06021828892 100644
> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -29,6 +29,7 @@
> #include <linux/kernel.h>
> #include <linux/math.h>
> #include <linux/mutex.h>
> +#include <linux/percpu.h>
> #include <linux/percpu-defs.h>
> #include <linux/printk.h>
> #include <linux/processor.h>
> @@ -170,6 +171,43 @@ static struct workqueue_struct *hfi_updates_wq;
> #define HFI_UPDATE_INTERVAL HZ
> #define HFI_MAX_THERM_NOTIFY_COUNT 16
>
> +#ifdef CONFIG_IPC_CLASSES

It would be good to provide a (concise) description of this variable.

> +static int __percpu *hfi_ipcc_scores;
> +
> +static int alloc_hfi_ipcc_scores(void)
> +{
> + if (!cpu_feature_enabled(X86_FEATURE_ITD))
> + return 0;
> +
> + hfi_ipcc_scores = __alloc_percpu(sizeof(*hfi_ipcc_scores) *
> + hfi_features.nr_classes,
> + sizeof(*hfi_ipcc_scores));
> +
> + return !hfi_ipcc_scores;

I would do

if (!hfi_ipcc_scores)
return -ENOMEM;

return 0;

Or make the function return bool.

> +}
> +
> +static void set_hfi_ipcc_score(void *caps, int cpu)
> +{
> + int i, *hfi_class;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_ITD))
> + return;
> +
> + hfi_class = per_cpu_ptr(hfi_ipcc_scores, cpu);
> +
> + for (i = 0; i < hfi_features.nr_classes; i++) {
> + struct hfi_cpu_data *class_caps;
> +
> + class_caps = caps + i * hfi_features.class_stride;
> + WRITE_ONCE(hfi_class[i], class_caps->perf_cap);

As it stands, it is unclear why WRITE_ONCE() is needed here.

> + }
> +}
> +
> +#else
> +static int alloc_hfi_ipcc_scores(void) { return 0; }
> +static void set_hfi_ipcc_score(void *caps, int cpu) { }
> +#endif /* CONFIG_IPC_CLASSES */
> +
> static void get_hfi_caps(struct hfi_instance *hfi_instance,
> struct thermal_genl_cpu_caps *cpu_caps)
> {
> @@ -192,6 +230,8 @@ static void get_hfi_caps(struct hfi_instance *hfi_instance,
> cpu_caps[i].efficiency = caps->ee_cap << 2;
>
> ++i;
> +
> + set_hfi_ipcc_score(caps, cpu);
> }
> raw_spin_unlock_irq(&hfi_instance->table_lock);
> }
> @@ -580,8 +620,14 @@ void __init intel_hfi_init(void)
> if (!hfi_updates_wq)
> goto err_nomem;
>
> + if (alloc_hfi_ipcc_scores())
> + goto err_ipcc;
> +
> return;
>
> +err_ipcc:
> + destroy_workqueue(hfi_updates_wq);
> +
> err_nomem:
> for (j = 0; j < i; ++j) {
> hfi_instance = &hfi_instances[j];
> --

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