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Date: Tue, 26 Jul 2022 20:31:10 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Jeremy Linton <jeremy.linton@....com>
Cc: Linux PM <linux-pm@...r.kernel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <lenb@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Robert Moore <robert.moore@...el.com>,
"open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI: CPPC: Disable FIE if registers in PCC regions
On Tue, Jul 26, 2022 at 5:00 PM Jeremy Linton <jeremy.linton@....com> 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@....com>
> ---
> drivers/acpi/cppc_acpi.c | 31 +++++++++++++++++++++++++++++++
> drivers/cpufreq/cppc_cpufreq.c | 19 +++++++++++++++----
> include/acpi/cppc_acpi.h | 5 +++++
> 3 files changed, 51 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 3c6d4ef87be0..ad84c55b6409 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1246,6 +1246,37 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
> }
> EXPORT_SYMBOL_GPL(cppc_get_perf_caps);
>
A kerneldoc, please.
> +int cppc_perf_ctrs_in_pcc(void)
Why int and not bool?
> +{
> + int cpu;
> + struct cpc_desc *cpc_desc;
> + struct cpc_register_resource *delivered_reg, *reference_reg,
> + *ref_perf_reg, *ctr_wrap_reg;
No line wraps here, please and follow the reverse xmas tree convention.
> +
> + for_each_present_cpu(cpu) {
Declare the variables only used in this loop here and you only need two.
> + cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> + delivered_reg = &cpc_desc->cpc_regs[DELIVERED_CTR];
> + reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];
> + ref_perf_reg = &cpc_desc->cpc_regs[REFERENCE_PERF];
> + ctr_wrap_reg = &cpc_desc->cpc_regs[CTR_WRAP_TIME];
I would do
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 (!CPC_SUPPORTED(ref_perf_reg))
ref_perf_reg = &cpc_desc->cpc_regs[NOMINAL_PERF];
if (CPC_IN_PCC(ref_perf_reg))
return true;
> +
> + /*
> + * 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];
> +
> + /* Are any of the regs PCC ?*/
> + if (CPC_IN_PCC(delivered_reg) || CPC_IN_PCC(reference_reg) ||
> + CPC_IN_PCC(ctr_wrap_reg) || 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..a66d3013d0f8 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -63,6 +63,10 @@ static struct cppc_workaround_oem_info wa_info[] = {
>
> static struct cpufreq_driver cppc_cpufreq_driver;
>
> +static bool fie_disabled;
> +module_param(fie_disabled, bool, 0444);
> +MODULE_PARM_DESC(fie_disabled, "Disable Frequency Invariance Engine (FIE)");
> +
> #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
>
> /* Frequency invariance support */
> @@ -158,7 +162,7 @@ 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 +203,7 @@ 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 +233,12 @@ static void __init cppc_freq_invariance_init(void)
> };
> int ret;
>
> - if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> + if (cppc_perf_ctrs_in_pcc()) {
> + pr_debug("FIE not enabled on systems with registers in PCC\n");
> + fie_disabled = true;
> + }
> +
> + if (fie_disabled)
> return;
>
> kworker_fie = kthread_create_worker(0, "cppc_fie");
> @@ -247,7 +256,7 @@ 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);
> @@ -940,6 +949,8 @@ static void cppc_check_hisi_workaround(void)
> }
> }
>
> + fie_disabled = true;
> +
> acpi_put_table(tbl);
> }
>
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index d389bab54241..f4ff571fcdcb 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 int 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;
> }
> +extern int cppc_perf_ctrs_in_pcc(void)
> +{
> + return false;
> +}
> static inline bool acpi_cpc_valid(void)
> {
> return false;
> --
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