[PATCH v1 3/3] ACPI: CPPC: Read CPC FFH counters in a single IPI

Vanshidhar Konda
2024-02-29T16:25:36Z

The CPPC driver reads delivered and reference counters using cpc_read
one at a time. This leads to inaccurate measurement of CPU frequency
discussed in [1]. If the firmware indicates that both the registers are
in the FFH interface the kernel can read the registers together in a
single IPI. This has two benefits:
1. Reduces the number of IPIs needed to read the two registers
2. The two registers will be read in close proximity resulting in more
accurate CPU frequency measurement

[1]: https://lore.kernel.org/all/20230328193846.8757-1-yang@os.amperecomputing.com/

Signed-off-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
---
arch/arm64/kernel/topology.c | 37 ++++++++++++++++++++++++++++++++++++
drivers/acpi/cppc_acpi.c | 32 +++++++++++++++++++++++++++----
include/acpi/cppc_acpi.h | 13 +++++++++++++
3 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 8905eb0c681f..8207565f43ee 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -421,6 +421,43 @@ int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val)
return ret;
}

+static void cpc_update_freq_counters(void *info)
+{
+ update_freq_counters_refs();
+}
+
+int cpc_read_regs_ffh(int cpu, struct ffh_cpc_reg_values *ffh_regs)
+{
+ struct amu_counters *ctrs = per_cpu_ptr(&cpu_samples, cpu);
+ int idx;
+
+ if (!cpc_ffh_supported() || !freq_counters_valid(cpu))
+ return -EOPNOTSUPP;
+
+ if (WARN_ON_ONCE(irqs_disabled()))
+ return -EPERM;
+
+ if (!idle_cpu(cpu))
+ smp_call_function_single(cpu, cpc_update_freq_counters, NULL, 1);
+
+ for (idx = 0; idx < MAX_NUM_CPC_REGS_FFH; idx++) {
+
+ if (!ffh_regs->regs[idx].reg)
+ continue;
+
+ switch ((u64)(ffh_regs->regs[idx].reg->address)) {
+ case 0x0:
+ ffh_regs->regs[idx].value = ctrs->core_cnt;
+ break;
+ case 0x1:
+ ffh_regs->regs[idx].value = ctrs->const_cnt;
+ break;
+ }
+ }
+
+ return 0;
+}
+
int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val)
{
return -EOPNOTSUPP;
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index d155a86a8614..55ffb1915e4f 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -113,6 +113,10 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
(cpc)->cpc_entry.reg.space_id == \
ACPI_ADR_SPACE_SYSTEM_IO)

+#define CPC_IN_FFH(cpc) ((cpc)->type == ACPI_TYPE_BUFFER && \
+ (cpc)->cpc_entry.reg.space_id == \
+ ACPI_ADR_SPACE_FIXED_HARDWARE)
+
/* Evaluates to True if reg is a NULL register descriptor */
#define IS_NULL_REG(reg) ((reg)->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY && \
(reg)->address == 0 && \
@@ -974,6 +978,11 @@ int __weak cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val)
return -ENOTSUPP;
}

+int __weak cpc_read_regs_ffh(int cpu, struct ffh_cpc_reg_values *regs)
+{
+ return -ENOTSUPP;
+}
+
/*
* Since cpc_read and cpc_write are called while holding pcc_lock, it should be
* as fast as possible. We have already mapped the PCC subspace during init, so
@@ -1317,7 +1326,7 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
struct cppc_pcc_data *pcc_ss_data = NULL;
u64 delivered, reference, ref_perf, ctr_wrap_time;
- int ret = 0, regs_in_pcc = 0;
+ int ret = 0, regs_in_pcc = 0, regs_read_in_ffh = 0;

if (!cpc_desc) {
pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
@@ -1353,8 +1362,23 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
}
}

- cpc_read(cpunum, delivered_reg, &delivered);
- cpc_read(cpunum, reference_reg, &reference);
+ if (CPC_IN_FFH(delivered_reg) && CPC_IN_FFH(reference_reg)) {
+ struct ffh_cpc_reg_values ffh_regs;
+
+ ffh_regs.regs[0].reg = &(delivered_reg->cpc_entry.reg);
+ ffh_regs.regs[1].reg = &(reference_reg->cpc_entry.reg);
+ ret = cpc_read_regs_ffh(cpunum, &ffh_regs);
+ if (!ret) {
+ delivered = ffh_regs.regs[0].value;
+ reference = ffh_regs.regs[1].value;
+ regs_read_in_ffh = 1;
+ }
+ }
+
+ if (!regs_read_in_ffh) {
+ cpc_read(cpunum, delivered_reg, &delivered);
+ cpc_read(cpunum, reference_reg, &reference);
+ }
cpc_read(cpunum, ref_perf_reg, &ref_perf);

/*
@@ -1366,7 +1390,7 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
if (CPC_SUPPORTED(ctr_wrap_reg))
cpc_read(cpunum, ctr_wrap_reg, &ctr_wrap_time);

- if (!delivered || !reference || !ref_perf) {
+ if (!delivered || !reference || !ref_perf) {
ret = -EFAULT;
goto out_err;
}
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 3a0995f8bce8..0da614a50edd 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -137,6 +137,18 @@ struct cppc_cpudata {
};

#ifdef CONFIG_ACPI_CPPC_LIB
+
+#define MAX_NUM_CPC_REGS_FFH 2
+
+struct ffh_cpc_reg {
+ struct cpc_reg *reg;
+ u64 value;
+};
+
+struct ffh_cpc_reg_values {
+ struct ffh_cpc_reg regs[MAX_NUM_CPC_REGS_FFH];
+};
+
extern int cppc_get_desired_perf(int cpunum, u64 *desired_perf);
extern int cppc_get_nominal_perf(int cpunum, u64 *nominal_perf);
extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs);
@@ -153,6 +165,7 @@ extern unsigned int cppc_get_transition_latency(int cpu);
extern bool cpc_ffh_supported(void);
extern bool cpc_supported_by_cpu(void);
extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val);
+extern int cpc_read_regs_ffh(int cpu, struct ffh_cpc_reg_values *regs);
extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
--
2.43.1