linux-kernel - [PATCH 2/3] arch_topology: obtain cpu capacity using information from CPPC

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Date:   Fri, 14 May 2021 10:53:38 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 2/3] arch_topology: obtain cpu capacity using information from CPPC

Define init_cpu_capacity_cppc() to use highest performance values
from _CPC objects to obtain and set maximum capacity information for
each CPU. acpi_cppc_processor_probe() is a good point at which to
trigger the initialization of CPU (u-arch) capacity values, as at this
point the highest performance values can be obtained from each CPU's
_CPC objects. Architectures can therefore use this functionality
through arch_init_invariance_cppc().

The performance scale used by CPPC is a unified scale for all CPUs in
the system. Therefore, by obtaining the raw highest performance values
from the _CPC objects, and normalizing them on the [0, 1024] capacity
scale, used by the task scheduler, we obtain the CPU capacity of each
CPU.

While an ACPI Notify(0x85) could alert about a change in the highest
performance value, which should in turn retrigger the CPU capacity
computations, this notification is not currently handled by the ACPI
processor driver. When supported, a call to arch_init_invariance_cppc()
would perform the update.

Signed-off-by: Ionela Voinescu <ionela.voinescu@....com>
Cc: Sudeep Holla <sudeep.holla@....com>
---
 drivers/base/arch_topology.c  | 39 +++++++++++++++++++++++++++++++++++
 include/linux/arch_topology.h |  4 ++++
 2 files changed, 43 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index c1179edc0f3b..f710d64f125b 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -291,6 +291,45 @@ bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
 	return !ret;
 }
 
+#ifdef CONFIG_ACPI_CPPC_LIB
+#include <acpi/cppc_acpi.h>
+
+void init_cpu_capacity_cppc(void)
+{
+	struct cppc_perf_caps perf_caps;
+	int cpu;
+
+	if (likely(acpi_disabled || !acpi_cpc_valid()))
+		return;
+
+	raw_capacity = kcalloc(num_possible_cpus(), sizeof(*raw_capacity),
+			       GFP_KERNEL);
+	if (!raw_capacity)
+		return;
+
+	for_each_possible_cpu(cpu) {
+		if (!cppc_get_perf_caps(cpu, &perf_caps)) {
+			raw_capacity[cpu] = perf_caps.highest_perf;
+			pr_debug("%s: CPU%d cpu_capacity=%u (raw).\n",
+				 __func__, cpu, raw_capacity[cpu]);
+		} else {
+			pr_err("%s: CPU%d missing highest performance.\n",
+				 __func__, cpu);
+			pr_err("%s: fallback to 1024 for all CPUs\n",
+				 __func__);
+			goto exit;
+		}
+	}
+
+	topology_normalize_cpu_scale();
+	schedule_work(&update_topology_flags_work);
+	pr_debug("%s: cpu_capacity initialization done\n", __func__);
+
+exit:
+	free_raw_capacity();
+}
+#endif
+
 #ifdef CONFIG_CPU_FREQ
 static cpumask_var_t cpus_to_visit;
 static void parsing_done_workfn(struct work_struct *work);
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index f180240dc95f..fbd829c3b7f7 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -11,6 +11,10 @@
 void topology_normalize_cpu_scale(void);
 int topology_update_cpu_topology(void);
 
+#ifdef CONFIG_ACPI_CPPC_LIB
+void init_cpu_capacity_cppc(void);
+#endif
+
 struct device_node;
 bool topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu);
 
-- 
2.29.2.dirty