diff options
Diffstat (limited to 'arch/x86/kernel/cpu/intel_epb.c')
| -rw-r--r-- | arch/x86/kernel/cpu/intel_epb.c | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/intel_epb.c b/arch/x86/kernel/cpu/intel_epb.c new file mode 100644 index 000000000000..f4dd73396f28 --- /dev/null +++ b/arch/x86/kernel/cpu/intel_epb.c @@ -0,0 +1,216 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Intel Performance and Energy Bias Hint support. + * + * Copyright (C) 2019 Intel Corporation + * + * Author: + * Rafael J. Wysocki <rafael.j.wysocki@intel.com> + */ + +#include <linux/cpuhotplug.h> +#include <linux/cpu.h> +#include <linux/device.h> +#include <linux/kernel.h> +#include <linux/string.h> +#include <linux/syscore_ops.h> +#include <linux/pm.h> + +#include <asm/cpufeature.h> +#include <asm/msr.h> + +/** + * DOC: overview + * + * The Performance and Energy Bias Hint (EPB) allows software to specify its + * preference with respect to the power-performance tradeoffs present in the + * processor. Generally, the EPB is expected to be set by user space (directly + * via sysfs or with the help of the x86_energy_perf_policy tool), but there are + * two reasons for the kernel to update it. + * + * First, there are systems where the platform firmware resets the EPB during + * system-wide transitions from sleep states back into the working state + * effectively causing the previous EPB updates by user space to be lost. + * Thus the kernel needs to save the current EPB values for all CPUs during + * system-wide transitions to sleep states and restore them on the way back to + * the working state. That can be achieved by saving EPB for secondary CPUs + * when they are taken offline during transitions into system sleep states and + * for the boot CPU in a syscore suspend operation, so that it can be restored + * for the boot CPU in a syscore resume operation and for the other CPUs when + * they are brought back online. However, CPUs that are already offline when + * a system-wide PM transition is started are not taken offline again, but their + * EPB values may still be reset by the platform firmware during the transition, + * so in fact it is necessary to save the EPB of any CPU taken offline and to + * restore it when the given CPU goes back online at all times. + * + * Second, on many systems the initial EPB value coming from the platform + * firmware is 0 ('performance') and at least on some of them that is because + * the platform firmware does not initialize EPB at all with the assumption that + * the OS will do that anyway. That sometimes is problematic, as it may cause + * the system battery to drain too fast, for example, so it is better to adjust + * it on CPU bring-up and if the initial EPB value for a given CPU is 0, the + * kernel changes it to 6 ('normal'). + */ + +static DEFINE_PER_CPU(u8, saved_epb); + +#define EPB_MASK 0x0fULL +#define EPB_SAVED 0x10ULL +#define MAX_EPB EPB_MASK + +static int intel_epb_save(void) +{ + u64 epb; + + rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb); + /* + * Ensure that saved_epb will always be nonzero after this write even if + * the EPB value read from the MSR is 0. + */ + this_cpu_write(saved_epb, (epb & EPB_MASK) | EPB_SAVED); + + return 0; +} + +static void intel_epb_restore(void) +{ + u64 val = this_cpu_read(saved_epb); + u64 epb; + + rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb); + if (val) { + val &= EPB_MASK; + } else { + /* + * Because intel_epb_save() has not run for the current CPU yet, + * it is going online for the first time, so if its EPB value is + * 0 ('performance') at this point, assume that it has not been + * initialized by the platform firmware and set it to 6 + * ('normal'). + */ + val = epb & EPB_MASK; + if (val == ENERGY_PERF_BIAS_PERFORMANCE) { + val = ENERGY_PERF_BIAS_NORMAL; + pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n"); + } + } + wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, (epb & ~EPB_MASK) | val); +} + +static struct syscore_ops intel_epb_syscore_ops = { + .suspend = intel_epb_save, + .resume = intel_epb_restore, +}; + +static const char * const energy_perf_strings[] = { + "performance", + "balance-performance", + "normal", + "balance-power", + "power" +}; +static const u8 energ_perf_values[] = { + ENERGY_PERF_BIAS_PERFORMANCE, + ENERGY_PERF_BIAS_BALANCE_PERFORMANCE, + ENERGY_PERF_BIAS_NORMAL, + ENERGY_PERF_BIAS_BALANCE_POWERSAVE, + ENERGY_PERF_BIAS_POWERSAVE +}; + +static ssize_t energy_perf_bias_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + unsigned int cpu = dev->id; + u64 epb; + int ret; + + ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb); + if (ret < 0) + return ret; + + return sprintf(buf, "%llu\n", epb); +} + +static ssize_t energy_perf_bias_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + unsigned int cpu = dev->id; + u64 epb, val; + int ret; + + ret = __sysfs_match_string(energy_perf_strings, + ARRAY_SIZE(energy_perf_strings), buf); + if (ret >= 0) + val = energ_perf_values[ret]; + else if (kstrtou64(buf, 0, &val) || val > MAX_EPB) + return -EINVAL; + + ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb); + if (ret < 0) + return ret; + + ret = wrmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, + (epb & ~EPB_MASK) | val); + if (ret < 0) + return ret; + + return count; +} + +static DEVICE_ATTR_RW(energy_perf_bias); + +static struct attribute *intel_epb_attrs[] = { + &dev_attr_energy_perf_bias.attr, + NULL +}; + +static const struct attribute_group intel_epb_attr_group = { + .name = power_group_name, + .attrs = intel_epb_attrs +}; + +static int intel_epb_online(unsigned int cpu) +{ + struct device *cpu_dev = get_cpu_device(cpu); + + intel_epb_restore(); + if (!cpuhp_tasks_frozen) + sysfs_merge_group(&cpu_dev->kobj, &intel_epb_attr_group); + + return 0; +} + +static int intel_epb_offline(unsigned int cpu) +{ + struct device *cpu_dev = get_cpu_device(cpu); + + if (!cpuhp_tasks_frozen) + sysfs_unmerge_group(&cpu_dev->kobj, &intel_epb_attr_group); + + intel_epb_save(); + return 0; +} + +static __init int intel_epb_init(void) +{ + int ret; + + if (!boot_cpu_has(X86_FEATURE_EPB)) + return -ENODEV; + + ret = cpuhp_setup_state(CPUHP_AP_X86_INTEL_EPB_ONLINE, + "x86/intel/epb:online", intel_epb_online, + intel_epb_offline); + if (ret < 0) + goto err_out_online; + + register_syscore_ops(&intel_epb_syscore_ops); + return 0; + +err_out_online: + cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE); + return ret; +} +subsys_initcall(intel_epb_init); |