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/[email protected]/
Signed-off-by: Vanshidhar Konda <[email protected]>
---
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
On Thu, Feb 29, 2024 at 5:25 PM Vanshidhar Konda
<[email protected]> wrote:
>
> 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/[email protected]/
>
> Signed-off-by: Vanshidhar Konda <[email protected]>
> ---
> 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;
> +}
This might return a bool value.
Is there any case in which the caller would handle different error
codes differently?
> +
> /*
> * 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;
Please use bool as the type for boolean variables.
>
> 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) {
If cpc_read_regs_ffh() returned 'true' on success, the above could be written as
if (cpc_read_regs_ffh(cpunum, &ffh_regs)) {
> + 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);
> --
On Thu, Feb 29, 2024 at 06:32:59PM +0100, Rafael J. Wysocki wrote:
>On Thu, Feb 29, 2024 at 5:25 PM Vanshidhar Konda
><[email protected]> wrote:
>>
>> 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/[email protected]/
>>
>> Signed-off-by: Vanshidhar Konda <[email protected]>
>> ---
>> 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;
>> +}
>
>This might return a bool value.
>
>Is there any case in which the caller would handle different error
>codes differently?
>
I kept this similar to cpc_read_ffh(). I didn't see any usage of the error
codes. The return value of cpc_read_ffh() is returned only from cpc_read(),
but I didn't see anyone consuming the return value of cpc_read().
Additionally, checkpatch complains about using -ENOTSUPP and suggests
replacing it with -EOPNOTSUPP. Does it make sense to update
cpc_read/write_ffh() as well to switch to return type bool?
>> +
>> /*
>> * 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;
>
>Please use bool as the type for boolean variables.
>
Thanks for pointing that out. I'll do that for the next version.
Thanks,
Vanshi
>>
>> 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) {
>
>If cpc_read_regs_ffh() returned 'true' on success, the above could be written as
>
>if (cpc_read_regs_ffh(cpunum, &ffh_regs)) {
>
>> + 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);
>> --
On Thu, Feb 29, 2024 at 7:01 PM Vanshidhar Konda
<[email protected]> wrote:
>
> On Thu, Feb 29, 2024 at 06:32:59PM +0100, Rafael J. Wysocki wrote:
> >On Thu, Feb 29, 2024 at 5:25 PM Vanshidhar Konda
> ><[email protected]> wrote:
> >>
> >> 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/[email protected]/
> >>
> >> Signed-off-by: Vanshidhar Konda <[email protected]>
> >> ---
> >> 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/topologyc
> >> 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;
> >> +}
> >
> >This might return a bool value.
> >
> >Is there any case in which the caller would handle different error
> >codes differently?
> >
> I kept this similar to cpc_read_ffh(). I didn't see any usage of the error
> codes. The return value of cpc_read_ffh() is returned only from cpc_read(),
> but I didn't see anyone consuming the return value of cpc_read().
> Additionally, checkpatch complains about using -ENOTSUPP and suggests
> replacing it with -EOPNOTSUPP. Does it make sense to update
> cpc_read/write_ffh() as well to switch to return type bool?
Probably, but in a separate patch.