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Message-ID: <CAJZ5v0jwW0=8cNvC-Vu_o+pEHFpN9nrPD4LXCpmSTgQBTHODgg@mail.gmail.com>
Date: Thu, 14 Dec 2023 20:31:17 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Huisong Li <lihuisong@...wei.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, rafael@...nel.org,
beata.michalska@....com, sumitg@...dia.com, ionela.voinescu@....com,
zengheng4@...wei.com, yang@...amperecomputing.com, will@...nel.org,
sudeep.holla@....com, liuyonglong@...wei.com, zhanjie9@...ilicon.com
Subject: Re: [PATCH] cpufreq: CPPC: Resolve the large frequency discrepancy
from cpuinfo_cur_freq
On Tue, Dec 12, 2023 at 8:26 AM Huisong Li <lihuisong@...wei.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@...wei.com>
First off, please Cc ACPI-related patches to linux-acpi.
> ---
> 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 ()?
> + 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
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.
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;
> --
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