[PATCH] cpufreq: CPPC: Resolve the large frequency discrepancy from cpuinfo_cur_freq
lihuisong (C)
lihuisong at huawei.com
Thu Dec 14 18:41:40 PST 2023
Hi Rafael,
Thanks for your review.😁
在 2023/12/15 3:31, Rafael J. Wysocki 写道:
> On Tue, Dec 12, 2023 at 8:26 AM Huisong Li <lihuisong at huawei.com> wrote:
>> Many developers found that the cpu current frequency is greater than
>> the maximum frequency of the platform, please see [1], [2] and [3].
>>
>> In the scenarios with high memory access pressure, the patch [1] has
>> proved the significant latency of cpc_read() which is used to obtain
>> delivered and reference performance counter cause an absurd frequency.
>> The sampling interval for this counters is very critical and is expected
>> to be equal. However, the different latency of cpc_read() has a direct
>> impact on their sampling interval.
>>
>> This patch adds a interface, cpc_read_arch_counters_on_cpu, to read
>> delivered and reference performance counter together. According to my
>> test[4], the discrepancy of cpu current frequency in the scenarios with
>> high memory access pressure is lower than 0.2% by stress-ng application.
>>
>> [1] https://lore.kernel.org/all/20231025093847.3740104-4-zengheng4@huawei.com/
>> [2] https://lore.kernel.org/all/20230328193846.8757-1-yang@os.amperecomputing.com/
>> [3] https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
>>
>> [4] My local test:
>> The testing platform enable SMT and include 128 logical CPU in total,
>> and CPU base frequency is 2.7GHz. Reading "cpuinfo_cur_freq" for each
>> physical core on platform during the high memory access pressure from
>> stress-ng, and the output is as follows:
>> 0: 2699133 2: 2699942 4: 2698189 6: 2704347
>> 8: 2704009 10: 2696277 12: 2702016 14: 2701388
>> 16: 2700358 18: 2696741 20: 2700091 22: 2700122
>> 24: 2701713 26: 2702025 28: 2699816 30: 2700121
>> 32: 2700000 34: 2699788 36: 2698884 38: 2699109
>> 40: 2704494 42: 2698350 44: 2699997 46: 2701023
>> 48: 2703448 50: 2699501 52: 2700000 54: 2699999
>> 56: 2702645 58: 2696923 60: 2697718 62: 2700547
>> 64: 2700313 66: 2700000 68: 2699904 70: 2699259
>> 72: 2699511 74: 2700644 76: 2702201 78: 2700000
>> 80: 2700776 82: 2700364 84: 2702674 86: 2700255
>> 88: 2699886 90: 2700359 92: 2699662 94: 2696188
>> 96: 2705454 98: 2699260 100: 2701097 102: 2699630
>> 104: 2700463 106: 2698408 108: 2697766 110: 2701181
>> 112: 2699166 114: 2701804 116: 2701907 118: 2701973
>> 120: 2699584 122: 2700474 124: 2700768 126: 2701963
>>
>> Signed-off-by: Huisong Li <lihuisong at huawei.com>
> First off, please Cc ACPI-related patches to linux-acpi.
got it.
+linux-acpi at vger.kernel.org
>
>> ---
>> arch/arm64/kernel/topology.c | 43 ++++++++++++++++++++++++++++++++++--
>> drivers/acpi/cppc_acpi.c | 22 +++++++++++++++---
>> include/acpi/cppc_acpi.h | 5 +++++
>> 3 files changed, 65 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
>> index 7d37e458e2f5..c3122154d738 100644
>> --- a/arch/arm64/kernel/topology.c
>> +++ b/arch/arm64/kernel/topology.c
>> @@ -299,6 +299,11 @@ core_initcall(init_amu_fie);
>> #ifdef CONFIG_ACPI_CPPC_LIB
>> #include <acpi/cppc_acpi.h>
>>
>> +struct amu_counters {
>> + u64 corecnt;
>> + u64 constcnt;
>> +};
>> +
>> static void cpu_read_corecnt(void *val)
>> {
>> /*
>> @@ -322,8 +327,27 @@ static void cpu_read_constcnt(void *val)
>> 0UL : read_constcnt();
>> }
>>
>> +static void cpu_read_amu_counters(void *data)
>> +{
>> + struct amu_counters *cnt = (struct amu_counters *)data;
>> +
>> + /*
>> + * The running time of the this_cpu_has_cap() might have a couple of
>> + * microseconds and is significantly increased to tens of microseconds.
>> + * But AMU core and constant counter need to be read togeter without any
>> + * time interval to reduce the calculation discrepancy using this counters.
>> + */
>> + if (this_cpu_has_cap(ARM64_WORKAROUND_2457168)) {
>> + cnt->corecnt = read_corecnt();
> This statement is present in both branches, so can it be moved before the if ()?
Yes.
Do you mean adding a blank line before if()?
>
>> + cnt->constcnt = 0;
>> + } else {
>> + cnt->corecnt = read_corecnt();
>> + cnt->constcnt = read_constcnt();
>> + }
>> +}
>> +
>> static inline
>> -int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val)
>> +int counters_read_on_cpu(int cpu, smp_call_func_t func, void *data)
>> {
>> /*
>> * Abort call on counterless CPU or when interrupts are
>> @@ -335,7 +359,7 @@ int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val)
>> if (WARN_ON_ONCE(irqs_disabled()))
>> return -EPERM;
>>
>> - smp_call_function_single(cpu, func, val, 1);
>> + smp_call_function_single(cpu, func, data, 1);
>>
>> return 0;
>> }
>> @@ -364,6 +388,21 @@ bool cpc_ffh_supported(void)
>> return true;
>> }
>>
>> +int cpc_read_arch_counters_on_cpu(int cpu, u64 *delivered, u64 *reference)
>> +{
>> + struct amu_counters cnts = {0};
>> + int ret;
>> +
>> + ret = counters_read_on_cpu(cpu, cpu_read_amu_counters, &cnts);
>> + if (ret)
>> + return ret;
>> +
>> + *delivered = cnts.corecnt;
>> + *reference = cnts.constcnt;
>> +
>> + return 0;
>> +}
>> +
>> int cpc_read_ffh(int cpu, struct cpc_reg *reg, u64 *val)
>> {
>> int ret = -EOPNOTSUPP;
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index 7ff269a78c20..f303fabd7cfe 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1299,6 +1299,11 @@ bool cppc_perf_ctrs_in_pcc(void)
>> }
>> EXPORT_SYMBOL_GPL(cppc_perf_ctrs_in_pcc);
>>
>> +int __weak cpc_read_arch_counters_on_cpu(int cpu, u64 *delivered, u64 *reference)
>> +{
>> + return 0;
>> +}
>> +
>> /**
>> * cppc_get_perf_ctrs - Read a CPU's performance feedback counters.
>> * @cpunum: CPU from which to read counters.
>> @@ -1313,7 +1318,8 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
>> *ref_perf_reg, *ctr_wrap_reg;
>> 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;
>> + u64 delivered = 0, reference = 0;
>> + u64 ref_perf, ctr_wrap_time;
>> int ret = 0, regs_in_pcc = 0;
>>
>> if (!cpc_desc) {
>> @@ -1350,8 +1356,18 @@ 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_ffh_supported()) {
>> + ret = cpc_read_arch_counters_on_cpu(cpunum, &delivered, &reference);
>> + if (ret) {
>> + pr_debug("read arch counters failed, ret=%d.\n", ret);
>> + ret = 0;
>> + }
>> + }
> The above is surely not applicable to every platform using CPPC. Also
cpc_ffh_supported is aimed to control only the platform supported FFH to enter.
cpc_read_arch_counters_on_cpu is also needed to implemented by each platform according to their require.
Here just implement this interface for arm64.
> it looks like in the ARM64_WORKAROUND_2457168 enabled case it is just
> pointless overhead, because "reference" is always going to be 0 here
> then.
Right, it is always going to be 0 here for the ARM64_WORKAROUND_2457168
enabled case .
But ARM64_WORKAROUND_2457168 is a macro releated to ARM.
It seems that it is not appropriate for this macro to appear this common
place for all platform, right?
>
> Please clean that up.
>
>> + if (!delivered || !reference) {
>> + cpc_read(cpunum, delivered_reg, &delivered);
>> + cpc_read(cpunum, reference_reg, &reference);
>> + }
>> +
>> cpc_read(cpunum, ref_perf_reg, &ref_perf);
>>
>> /*
>> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
>> index 6126c977ece0..07d4fd82d499 100644
>> --- a/include/acpi/cppc_acpi.h
>> +++ b/include/acpi/cppc_acpi.h
>> @@ -152,6 +152,7 @@ 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_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
>> +extern int cpc_read_arch_counters_on_cpu(int cpu, u64 *delivered, u64 *reference);
>> 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);
>> extern int cppc_get_auto_sel_caps(int cpunum, struct cppc_perf_caps *perf_caps);
>> @@ -209,6 +210,10 @@ static inline int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val)
>> {
>> return -ENOTSUPP;
>> }
>> +static inline int cpc_read_arch_counters_on_cpu(int cpu, u64 *delivered, u64 *reference)
>> +{
>> + return -EOPNOTSUPP;
>> +}
>> static inline int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>> {
>> return -ENOTSUPP;
>> --
> .
More information about the linux-arm-kernel
mailing list