[PATCH v2 1/1] ACPI: CPPC: Disable FIE if registers in PCC regions

Jeremy Linton
2022-07-28T22:11:41Z

PCC regions utilize a mailbox to set/retrieve register values used by
the CPPC code. This is fine as long as the operations are
infrequent. With the FIE code enabled though the overhead can range
from 2-11% of system CPU overhead (ex: as measured by top) on Arm
based machines.

So, before enabling FIE assure none of the registers used by
cppc_get_perf_ctrs() are in the PCC region. Furthermore lets also
enable a module parameter which can also disable it at boot or module
reload.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
---
drivers/acpi/cppc_acpi.c | 41 ++++++++++++++++++++++++++++++++++
drivers/cpufreq/cppc_cpufreq.c | 19 ++++++++++++----
include/acpi/cppc_acpi.h | 5 +++++
3 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 3c6d4ef87be0..38b881db14c7 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1246,6 +1246,47 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
}
EXPORT_SYMBOL_GPL(cppc_get_perf_caps);

+/**
+ * cppc_perf_ctrs_in_pcc - Check if any perf counters are in a PCC region.
+ *
+ * CPPC has flexibility about how counters describing CPU perf are delivered.
+ * One of the choices is PCC regions, which can have a high access latency. This
+ * routine allows callers of cppc_get_perf_ctrs() to know this ahead of time.
+ *
+ * Return: true if any of the counters are in PCC regions, false otherwise
+ */
+bool cppc_perf_ctrs_in_pcc(void)
+{
+ int cpu;
+
+ for_each_present_cpu(cpu) {
+ struct cpc_register_resource *ref_perf_reg;
+ struct cpc_desc *cpc_desc;
+
+ cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+
+ if (CPC_IN_PCC(&cpc_desc->cpc_regs[DELIVERED_CTR]) ||
+ CPC_IN_PCC(&cpc_desc->cpc_regs[REFERENCE_CTR]) ||
+ CPC_IN_PCC(&cpc_desc->cpc_regs[CTR_WRAP_TIME]))
+ return true;
+
+
+ ref_perf_reg = &cpc_desc->cpc_regs[REFERENCE_PERF];
+
+ /*
+ * If reference perf register is not supported then we should
+ * use the nominal perf value
+ */
+ if (!CPC_SUPPORTED(ref_perf_reg))
+ ref_perf_reg = &cpc_desc->cpc_regs[NOMINAL_PERF];
+
+ if (CPC_IN_PCC(ref_perf_reg))
+ return true;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(cppc_perf_ctrs_in_pcc);
+
/**
* cppc_get_perf_ctrs - Read a CPU's performance feedback counters.
* @cpunum: CPU from which to read counters.
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 24eaf0ec344d..ed607e27d6bb 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -63,7 +63,11 @@ static struct cppc_workaround_oem_info wa_info[] = {

static struct cpufreq_driver cppc_cpufreq_driver;

+static bool fie_disabled;
+
#ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
+module_param(fie_disabled, bool, 0444);
+MODULE_PARM_DESC(fie_disabled, "Disable Frequency Invariance Engine (FIE)");

/* Frequency invariance support */
struct cppc_freq_invariance {
@@ -158,7 +162,7 @@ static void cppc_cpufreq_cpu_fie_init(struct cpufreq_policy *policy)
struct cppc_freq_invariance *cppc_fi;
int cpu, ret;

- if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
+ if (fie_disabled)
return;

for_each_cpu(cpu, policy->cpus) {
@@ -199,7 +203,7 @@ static void cppc_cpufreq_cpu_fie_exit(struct cpufreq_policy *policy)
struct cppc_freq_invariance *cppc_fi;
int cpu;

- if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
+ if (fie_disabled)
return;

/* policy->cpus will be empty here, use related_cpus instead */
@@ -229,7 +233,12 @@ static void __init cppc_freq_invariance_init(void)
};
int ret;

- if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
+ if (cppc_perf_ctrs_in_pcc()) {
+ pr_debug("FIE not enabled on systems with registers in PCC\n");
+ fie_disabled = true;
+ }
+
+ if (fie_disabled)
return;

kworker_fie = kthread_create_worker(0, "cppc_fie");
@@ -247,7 +256,7 @@ static void __init cppc_freq_invariance_init(void)

static void cppc_freq_invariance_exit(void)
{
- if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
+ if (fie_disabled)
return;

kthread_destroy_worker(kworker_fie);
@@ -940,6 +949,8 @@ static void cppc_check_hisi_workaround(void)
}
}

+ fie_disabled = true;
+
acpi_put_table(tbl);
}

diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index d389bab54241..fe6dc3e5a454 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -140,6 +140,7 @@ extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs);
extern int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls);
extern int cppc_set_enable(int cpu, bool enable);
extern int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps);
+extern bool cppc_perf_ctrs_in_pcc(void);
extern bool acpi_cpc_valid(void);
extern bool cppc_allow_fast_switch(void);
extern int acpi_get_psd_map(unsigned int cpu, struct cppc_cpudata *cpu_data);
@@ -173,6 +174,10 @@ static inline int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps)
{
return -ENOTSUPP;
}
+static inline bool cppc_perf_ctrs_in_pcc(void)
+{
+ return false;
+}
static inline bool acpi_cpc_valid(void)
{
return false;
--
2.35.3