Re: [PATCH v3 1/2] ACPI: CPPC: Disable FIE if registers in PCC regions
From: Jeremy Linton
Date: Tue Aug 23 2022 - 15:44:46 EST
Hi,
On 8/23/22 12:10, Rafael J. Wysocki wrote:
On Thu, Aug 18, 2022 at 11:24 PM Jeremy Linton <jeremy.linton@xxxxxxx> wrote:
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@xxxxxxx>
---
drivers/acpi/cppc_acpi.c | 41 ++++++++++++++++++++++++++++++++++
drivers/cpufreq/cppc_cpufreq.c | 31 +++++++++++++++++++++----
include/acpi/cppc_acpi.h | 5 +++++
3 files changed, 73 insertions(+), 4 deletions(-)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 1e15a9f25ae9..c840bf606b30 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1240,6 +1240,47 @@ 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.
"CPU performance counters are accessed"
Sure,
+ * 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..32fcb0bf74a4 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -63,7 +63,15 @@ static struct cppc_workaround_oem_info wa_info[] = {
static struct cpufreq_driver cppc_cpufreq_driver;
+static enum {
+ FIE_UNSET = -1,
+ FIE_ENABLED,
+ FIE_DISABLED
+} fie_disabled = FIE_UNSET;
+
#ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
+module_param(fie_disabled, int, 0444);
+MODULE_PARM_DESC(fie_disabled, "Disable Frequency Invariance Engine (FIE)");
/* Frequency invariance support */
struct cppc_freq_invariance {
@@ -158,7 +166,7 @@ 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 +207,7 @@ 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 +237,21 @@ static void __init cppc_freq_invariance_init(void)
};
int ret;
- if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
+ switch (fie_disabled) {
+ /* honor user request */
+ case FIE_DISABLED:
+ case FIE_ENABLED:
+ break;
+ case FIE_UNSET:
+ default:
Would be more straightforward to do
if (fie_disabled == FIE_UNSET) {
here.
Right, but then it wouldn't catch the other billion+ values that are the
result of not being able to export a limit (AFAIK) on the module
parameter. I could use an if:
if !((fie_disabled == FIE_DISABLE) || (fie_disabled == FIE_ENABLED)) {
}
if that is preferable. I thought the case with the explict default:
though made it clearer that it was treating all those other values as unset.
+ fie_disabled = FIE_ENABLED;
+ if (cppc_perf_ctrs_in_pcc()) {
+ pr_info("FIE not enabled on systems with registers in PCC\n");
+ fie_disabled = FIE_DISABLED;
+ }
+ break;
+ }
+ if (fie_disabled)
return;
kworker_fie = kthread_create_worker(0, "cppc_fie");
@@ -247,7 +269,7 @@ 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);
@@ -936,6 +958,7 @@ static void cppc_check_hisi_workaround(void)
wa_info[i].oem_revision == tbl->oem_revision) {
/* Overwrite the get() callback */
cppc_cpufreq_driver.get = hisi_cppc_cpufreq_get_rate;
+ fie_disabled = FIE_DISABLED;
break;
}
}
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index f73d357ecdf5..c5614444031f 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;
--
Apart from the above it looks fine to me, but I would like to get an
ACK from Viresh on the second patch.
Thanks!
Thanks for looking at this.