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

* [PATCH] ACPI: CPPC: Disable FIE if registers in PCC regions
@ 2022-07-26 14:59 Jeremy Linton
  2022-07-26 18:31 ` Rafael J. Wysocki
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Jeremy Linton @ 2022-07-26 14:59 UTC (permalink / raw)
  To: linux-pm
  Cc: rafael, lenb, viresh.kumar, robert.moore, devel, linux-acpi,
	linux-kernel, Jeremy Linton

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       | 31 +++++++++++++++++++++++++++++++
 drivers/cpufreq/cppc_cpufreq.c | 19 +++++++++++++++----
 include/acpi/cppc_acpi.h       |  5 +++++
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 3c6d4ef87be0..ad84c55b6409 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1246,6 +1246,37 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
 }
 EXPORT_SYMBOL_GPL(cppc_get_perf_caps);
 
+int cppc_perf_ctrs_in_pcc(void)
+{
+	int cpu;
+	struct cpc_desc *cpc_desc;
+	struct cpc_register_resource *delivered_reg, *reference_reg,
+		*ref_perf_reg, *ctr_wrap_reg;
+
+	for_each_present_cpu(cpu) {
+		cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+		delivered_reg = &cpc_desc->cpc_regs[DELIVERED_CTR];
+		reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];
+		ref_perf_reg = &cpc_desc->cpc_regs[REFERENCE_PERF];
+		ctr_wrap_reg = &cpc_desc->cpc_regs[CTR_WRAP_TIME];
+
+		/*
+		 * 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];
+
+		/* Are any of the regs PCC ?*/
+		if (CPC_IN_PCC(delivered_reg) || CPC_IN_PCC(reference_reg) ||
+			CPC_IN_PCC(ctr_wrap_reg) || 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..a66d3013d0f8 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -63,6 +63,10 @@ static struct cppc_workaround_oem_info wa_info[] = {
 
 static struct cpufreq_driver cppc_cpufreq_driver;
 
+static bool fie_disabled;
+module_param(fie_disabled, bool, 0444);
+MODULE_PARM_DESC(fie_disabled, "Disable Frequency Invariance Engine (FIE)");
+
 #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
 
 /* Frequency invariance support */
@@ -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..f4ff571fcdcb 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 int 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;
 }
+extern int cppc_perf_ctrs_in_pcc(void)
+{
+	return false;
+}
 static inline bool acpi_cpc_valid(void)
 {
 	return false;
-- 
2.37.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread