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SubjectRe: [RFC PATCH] thermal: add generic cpu hotplug cooling device
From
Any comments on this proposed feature and implementation? Apparently
it's also useful for server systems.
Thanks,
Zoran

On 20 September 2013 15:15, Zoran Markovic <zoran.markovic@linaro.org> wrote:
> This patch implements a generic CPU hotplug cooling device. The
> implementation scales down the number of running CPUs when temperature
> increases through a thermal trip point and prevents booting CPUs
> until thermal conditions are restored. Upon restoration, the action
> of starting up a CPU is left to another entity (e.g. CPU offline
> governor, for which a patch is in the works).
>
> In the past two years, ARM considerably reduced the time required for
> CPUs to boot and shutdown; this time is now measured in microseconds.
> This patch is predominantly intended for ARM big.LITTLE architectures
> where big cores are expected to have a much bigger impact on thermal
> budget than little cores, resulting in fast temperature ramps to a trip
> point, i.e. thermal runaways. Switching off the big core(s) may be one
> of the recovery mechanisms to restore system temperature, but the actual
> strategy is left to the thermal governor.
>
> The assumption is that CPU shutdown/startup is a rare event, so no
> attempt was made to make the code atomic, i.e. the code evidently races
> with CPU hotplug driver. The set_cur_state() function offlines CPUs
> iteratively one at a time, checking the cooling state before each CPU
> shutdown. A hotplug notifier callback validates any CPU boot requests
> against current cooling state and approves/denies accordingly. This
> mechanism guarantees that the desired cooling state could be reached in a
> maximum of d-c iterations, where d and c are the "desired" and "current"
> cooling states expressed in the number of offline CPUs.
>
> Credits to Amit Daniel Kachhap for initial attempt to upstream this feature.
>
> Cc: Zhang Rui <rui.zhang@intel.com>
> Cc: Eduardo Valentin <eduardo.valentin@ti.com>
> Cc: Rob Landley <rob@landley.net>
> Cc: Amit Daniel Kachhap <amit.daniel@samsung.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Durgadoss R <durgadoss.r@intel.com>
> Cc: Christian Daudt <bcm@fixthebug.org>
> Cc: James King <james.king@linaro.org>
> Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
> ---
> Documentation/thermal/cpu-cooling-api.txt | 17 ++
> drivers/thermal/Kconfig | 10 +
> drivers/thermal/Makefile | 1 +
> drivers/thermal/cpu_hotplug.c | 362 +++++++++++++++++++++++++++++
> include/linux/cpuhp_cooling.h | 57 +++++
> 5 files changed, 447 insertions(+)
> create mode 100644 drivers/thermal/cpu_hotplug.c
> create mode 100644 include/linux/cpuhp_cooling.h
>
> diff --git a/Documentation/thermal/cpu-cooling-api.txt b/Documentation/thermal/cpu-cooling-api.txt
> index fca24c9..2f94f68 100644
> --- a/Documentation/thermal/cpu-cooling-api.txt
> +++ b/Documentation/thermal/cpu-cooling-api.txt
> @@ -30,3 +30,20 @@ the user. The registration APIs returns the cooling device pointer.
> This interface function unregisters the "thermal-cpufreq-%x" cooling device.
>
> cdev: Cooling device pointer which has to be unregistered.
> +
> +1.2 cpu hotplug registration/unregistration APIs
> +1.2.1 struct thermal_cooling_device *cpuhp_cooling_register(
> + struct cpumask *cpus, const char *ext)
> +
> + This function creates and registers a cpu hotplug cooling device with
> + the name "cpu-hotplug-%s".
> +
> + cpus: cpumask of cpu cores participating in cooling.
> + ext: instance-specific name of device
> +
> +1.2.2 void cpuhotplug_cooling_unregister(struct thermal_cooling_device *cdev)
> +
> + This function unregisters and frees the cpu hotplug cooling device cdev.
> +
> + cdev: Pointer to cooling device to unregister.
> +
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 52b6ed7..3509100 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -79,6 +79,16 @@ config CPU_THERMAL
>
> If you want this support, you should say Y here.
>
> +config CPU_THERMAL_HOTPLUG
> + bool "Generic CPU hotplug cooling"
> + depends on HOTPLUG_CPU
> + help
> + Shutdown CPUs to prevent the device from overheating. This feature
> + uses generic CPU hot-unplug capabilities to control device
> + temperature. When the temperature increases over a trip point, a
> + random subset of CPUs is shut down to reach the desired cooling
> + state.
> +
> config THERMAL_EMULATION
> bool "Thermal emulation mode support"
> help
> diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> index 5ee0db0..0bd08be 100644
> --- a/drivers/thermal/Makefile
> +++ b/drivers/thermal/Makefile
> @@ -12,6 +12,7 @@ thermal_sys-$(CONFIG_THERMAL_GOV_USER_SPACE) += user_space.o
>
> # cpufreq cooling
> thermal_sys-$(CONFIG_CPU_THERMAL) += cpu_cooling.o
> +thermal_sys-$(CONFIG_CPU_THERMAL_HOTPLUG) += cpu_hotplug.o
>
> # platform thermal drivers
> obj-$(CONFIG_SPEAR_THERMAL) += spear_thermal.o
> diff --git a/drivers/thermal/cpu_hotplug.c b/drivers/thermal/cpu_hotplug.c
> new file mode 100644
> index 0000000..8c3021e
> --- /dev/null
> +++ b/drivers/thermal/cpu_hotplug.c
> @@ -0,0 +1,362 @@
> +/*
> + * drivers/thermal/cpu_hotplug.c
> + *
> + * Copyright (C) 2013 Broadcom Corporation Ltd.
> + * Copyright (C) 2013 Zoran Markovic <zoran.markovic@linaro.org>
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; version 2 of the License.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, write to the Free Software Foundation, Inc.,
> + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + */
> +#include <linux/module.h>
> +#include <linux/thermal.h>
> +#include <linux/workqueue.h>
> +#include <linux/cpu.h>
> +#include <linux/err.h>
> +#include <linux/slab.h>
> +#include <linux/cpuhp_cooling.h>
> +
> +/**
> + * struct cpuhotplug_cooling_device - cpu hotplug cooling device data
> + * @cpus: cpu mask representing cpus that can be hot-unplugged for cooling
> + * @cdev: pointer to generic cooling device
> + */
> +struct cpuhotplug_cooling_device {
> + unsigned int target;
> + struct cpumask cpus;
> + struct thermal_cooling_device *cdev;
> + struct list_head list;
> +};
> +
> +/**
> + * cpuhotplug_list - list of all cpu hotplug cooling devices. Traversed
> + * by cpu hotplug notifier to check constraints on booting cpus. Locked
> + * by cpuhotplug_cooling_lock mutex.
> + */
> +static LIST_HEAD(cpuhotplug_list);
> +static DEFINE_MUTEX(cpuhotplug_cooling_lock);
> +
> +/**
> + * boot_cpu - return index of boot CPU; same criteria as in
> + * disable_nonboot_cpus()
> + */
> +static inline int boot_cpu(void)
> +{
> + int cpu;
> + get_online_cpus();
> + cpu = cpumask_first(cpu_online_mask);
> + put_online_cpus();
> + return cpu;
> +}
> +
> +/**
> + * random_online_cpu - pick any online hot-unpluggable cpu
> + * @d: pointer to cpuhotplug_cooling_device containing hot-pluggable cpu mask
> + */
> +static inline int random_online_cpu(struct cpuhotplug_cooling_device *d)
> +{
> + int cpu;
> +
> + get_online_cpus();
> + cpu = any_online_cpu(d->cpus);
> + put_online_cpus();
> +
> + return cpu;
> +}
> +
> +/**
> + * _num_offline_cpus - number of hot-pluggable cpus currently offline
> + * @d: pointer to cpuhotplug_cooling_device containing hot-pluggable cpu mask
> + */
> +static inline int _num_offline_cpus(struct cpuhotplug_cooling_device *d)
> +{
> + struct cpumask offline;
> +
> + cpumask_andnot(&offline, &(d->cpus), cpu_online_mask);
> + return cpumask_weight(&offline);
> +}
> +
> +/**
> + * num_offline_cpus - same as _num_offline_cpus, but safe from background
> + * hotplug events.
> + * @d: pointer to cpuhotplug_cooling_device containing hot-pluggable cpu mask
> + */
> +static inline int num_offline_cpus(struct cpuhotplug_cooling_device *d)
> +{
> + int num;
> +
> + get_online_cpus();
> + num = _num_offline_cpus(d);
> + put_online_cpus();
> +
> + return num;
> +}
> +
> +/**
> + * cpuhotplug_get_max_state - get maximum cooling state of device
> + * @cdev: pointer to generic cooling device
> + * @state: returned maximum cooling state
> + *
> + * Thermal framework callback to get the maximum cooling state of cpu
> + * hotplug cooling device.
> + *
> + * Return: always 0.
> + */
> +static int cpuhotplug_get_max_state(struct thermal_cooling_device *cdev,
> + unsigned long *state)
> +{
> + struct cpuhotplug_cooling_device *d = cdev->devdata;
> +
> + /* defined as number of CPUs in hot-pluggable mask: this is invariant */
> + *state = cpumask_weight(&(d->cpus));
> +
> + return 0;
> +}
> +
> +/**
> + * cpuhotplug_get_cur_state - get current cooling state of device
> + * @cdev: pointer to generic cooling device
> + * @state: current cooling state
> + *
> + * Thermal framework callback to get the current cooling state of cpu
> + * hotplug cooling device.
> + *
> + * Return: always 0.
> + */
> +static int cpuhotplug_get_cur_state(struct thermal_cooling_device *cdev,
> + unsigned long *state)
> +{
> + struct cpuhotplug_cooling_device *d = cdev->devdata;
> +
> + *state = d->target;
> +
> + return 0;
> +}
> +
> +/**
> + * cpuhotplug_get_cur_state - set cooling state of device
> + * @cdev: pointer to generic cooling device
> + * @state: cooling state
> + *
> + * Thermal framework callback to set/change cooling state of cpu hotplug
> + * cooling device.
> + *
> + * Return: 0 on success, or error code otherwise
> + */
> +static int cpuhotplug_set_cur_state(struct thermal_cooling_device *cdev,
> + unsigned long state)
> +{
> + struct cpuhotplug_cooling_device *d = cdev->devdata;
> + unsigned long cstate;
> + unsigned int cpu;
> + int err = 0;
> +
> + if (state > cpumask_weight(&(d->cpus)))
> + return -EINVAL; /* out of allowed range */
> +
> + /*
> + * Set target state here; hot-unplug CPUs if we are too hot, but
> + * don't attempt to hot-plug CPUs if we're cold. Starting CPUs
> + * should be left to CPUOffline governor.
> + *
> + * There is a chance that CPU hotplug driver is racing with this
> + * code. Rather than trying to make the procedure atomic, iterate
> + * until we reach the desired state, or signal error if the state
> + * cannot be reached.
> + *
> + * Neither CPU hotplug nor this code is expected to run too often.
> + */
> + d->target = state;
> +
> + /* compare desired cooling state to current cooling state */
> + while ((cstate = num_offline_cpus(d)) < state && !err) {
> + /* cstate < cstate: we're too hot, unplug any cpu */
> + cpu = random_online_cpu(d);
> + if (cpu < nr_cpu_ids)
> + err = work_on_cpu(boot_cpu(),
> + (long(*)(void *))cpu_down,
> + (void *)cpu);
> + /* on error, message would come from cpu_down() */
> + else {
> + pr_warn("cpuhotplug: CPUs already down\n");
> + err = -EAGAIN;
> + }
> + }
> +
> + return err;
> +}
> +
> +/* cpu hotplug cooling device ops */
> +static struct thermal_cooling_device_ops const cpuhotplug_cooling_ops = {
> + .get_max_state = cpuhotplug_get_max_state,
> + .get_cur_state = cpuhotplug_get_cur_state,
> + .set_cur_state = cpuhotplug_set_cur_state,
> +};
> +
> +/**
> + * _cpu_startup_allowed - traverse list of hotplug cooling devices to
> + * check if startup of cpu violates thermal constraints
> + */
> +static inline int _cpu_startup_allowed(int cpu)
> +{
> + struct cpuhotplug_cooling_device *d;
> + int ret = 1;
> +
> + /*
> + * Prevent starting CPU if it violates any cooling
> + * device's constraint. Called from hotplug notifier, so
> + * cpu_up()/cpu_down() already holds a lock on hotplug
> + * events.
> + */
> + mutex_lock(&cpuhotplug_cooling_lock);
> + list_for_each_entry(d, &cpuhotplug_list, list) {
> + if (cpumask_test_cpu(cpu, &(d->cpus)) &&
> + d->target >= _num_offline_cpus(d)) {
> + pr_warn("%s: CPU%d startup prevented\n",
> + dev_name(&(d->cdev->device)), cpu);
> + ret = 0;
> + break;
> + }
> + }
> + mutex_unlock(&cpuhotplug_cooling_lock);
> + return ret;
> +}
> +
> +/**
> + * cpuhotplug_thermal_notifier - notifier callback for CPU hotplug events.
> + * @nb: struct notifier_block
> + * @event: cpu hotplug event for which callback is invoked.
> + * @data: context data, in this particular case CPU index.
> + *
> + * Callback intercepting CPU hotplug events. Compares CPU hotplug action
> + * with current thermal state and allows/denies accordingly.
> + *
> + * Return: 0 (allow) or error (deny).
> + */
> +static int cpuhotplug_thermal_notifier(struct notifier_block *nb,
> + unsigned long event, void *data)
> +{
> + int cpu = (int)data;
> +
> + switch (event) {
> + case CPU_UP_PREPARE:
> + case CPU_UP_PREPARE_FROZEN:
> + /* _cpu_up() only cares about result from CPU_UP_PREPAREs */
> + if (!_cpu_startup_allowed(cpu))
> + return notifier_from_errno(-EAGAIN);
> + break;
> + default:
> + /* allow all other actions */
> + break;
> + }
> + return 0;
> +}
> +
> +static struct notifier_block cpuhotplug_thermal_notifier_block = {
> + .notifier_call = cpuhotplug_thermal_notifier,
> +};
> +
> +/**
> + * cpuhotplug_cooling_register - create cpu hotplug cooling device
> + * @cpus: cpumask of cpu cores participating in cooling
> + * @ext: instance-specific name of device
> + *
> + * Creates and registers a cpu hotplug cooling device with the name
> + * "cpu-hotplug-<ext>".
> + *
> + * Return: valid pointer to cpuhotplug_cooling_device struct on success,
> + * corresponding ERR_PTR() on failure.
> + */
> +struct thermal_cooling_device *
> +cpuhotplug_cooling_register(const struct cpumask *cpus, const char *ext)
> +{
> + struct thermal_cooling_device *cdev;
> + struct cpuhotplug_cooling_device *cpuhotplug_cdev;
> + struct cpumask test;
> + char name[THERMAL_NAME_LENGTH];
> + int err;
> +
> + /* test if we passed in a good cpumask */
> + cpu_maps_update_begin();
> + cpumask_and(&test, cpus, cpu_possible_mask);
> + cpu_maps_update_done();
> +
> + if (cpumask_test_cpu(boot_cpu(), &test)) {
> + pr_warn("cannot hot-plug boot CPU%d\n", boot_cpu());
> + cpumask_clear_cpu(boot_cpu(), &test);
> + }
> + if (cpumask_empty(&test)) {
> + pr_err("CPUs unavailable for hot-plug cooling\n");
> + err = -EINVAL;
> + goto out;
> + }
> +
> + cpuhotplug_cdev = kzalloc(sizeof(struct cpuhotplug_cooling_device),
> + GFP_KERNEL);
> + if (!cpuhotplug_cdev) {
> + err = -ENOMEM;
> + goto out;
> + }
> +
> + cpumask_copy(&cpuhotplug_cdev->cpus, &test);
> +
> + snprintf(name, sizeof(name), "cpu-hotplug-%s", ext);
> +
> + cpuhotplug_cdev->target = 0;
> + cdev = thermal_cooling_device_register(name, cpuhotplug_cdev,
> + &cpuhotplug_cooling_ops);
> + if (!cdev) {
> + pr_err("%s: cooling device registration failed.\n", name);
> + err = -EINVAL;
> + goto out_free;
> + }
> + cpuhotplug_cdev->cdev = cdev;
> +
> + mutex_lock(&cpuhotplug_cooling_lock);
> + if (list_empty(&cpuhotplug_list))
> + register_cpu_notifier(&cpuhotplug_thermal_notifier_block);
> + list_add(&(cpuhotplug_cdev->list), &cpuhotplug_list);
> + mutex_unlock(&cpuhotplug_cooling_lock);
> +
> + return cdev;
> +
> +out_free:
> + kfree(cpuhotplug_cdev);
> +out:
> + return ERR_PTR(err);
> +}
> +EXPORT_SYMBOL_GPL(cpuhotplug_cooling_register);
> +
> +/**
> + * cpuhotplug_cooling_unregister - remove cpu hotplug cooling device
> + * @cdev: cooling device to remove
> + *
> + * Unregisters and frees the cpu hotplug cooling device.
> + */
> +void cpuhotplug_cooling_unregister(struct thermal_cooling_device *cdev)
> +{
> + struct cpuhotplug_cooling_device *cpuhotplug_cdev = cdev->devdata;
> +
> + mutex_lock(&cpuhotplug_cooling_lock);
> + list_del(&(cpuhotplug_cdev->list));
> + if (list_empty(&cpuhotplug_list))
> + unregister_cpu_notifier(&cpuhotplug_thermal_notifier_block);
> + mutex_unlock(&cpuhotplug_cooling_lock);
> +
> + thermal_cooling_device_unregister(cpuhotplug_cdev->cdev);
> + kfree(cpuhotplug_cdev);
> +}
> +EXPORT_SYMBOL_GPL(cpuhotplug_cooling_unregister);
> +
> diff --git a/include/linux/cpuhp_cooling.h b/include/linux/cpuhp_cooling.h
> new file mode 100644
> index 0000000..ace1d5b
> --- /dev/null
> +++ b/include/linux/cpuhp_cooling.h
> @@ -0,0 +1,57 @@
> +/*
> + * linux/include/linux/cpuhp_cooling.h
> + *
> + * Copyright (C) 2013 Broadcom Corporation Ltd.
> + * Copyright (C) 2013 Zoran Markovic <zoran.markovic@linaro.org>
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; version 2 of the License.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, write to the Free Software Foundation, Inc.,
> + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
> + *
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + */
> +
> +#ifndef __CPUHP_COOLING_H__
> +#define __CPUHP_COOLING_H__
> +
> +#include <linux/thermal.h>
> +#include <linux/cpumask.h>
> +
> +#ifdef CONFIG_CPU_THERMAL_HOTPLUG
> +/**
> + * cpuhotplug_cooling_register - create cpu hotplug cooling device.
> + * @cpus: cpumask of hot-pluggable cpus
> + * @ext: instance-specific device name
> + */
> +struct thermal_cooling_device *
> +cpuhotplug_cooling_register(const struct cpumask *cpus, const char *ext);
> +
> +/**
> + * cpuhotplug_cooling_unregister - remove cpu hoptlug cooling device.
> + * @cdev: thermal cooling device pointer.
> + */
> +void cpuhotplug_cooling_unregister(struct thermal_cooling_device *cdev);
> +#else /* !CONFIG_CPU_THERMAL_HOTPLUG */
> +static inline struct thermal_cooling_device *
> +cpuhotplug_cooling_register(const struct cpumask *cpus, const char *ext)
> +{
> + return NULL;
> +}
> +static inline
> +void cpuhotplug_cooling_unregister(struct thermal_cooling_device *cdev)
> +{
> + return;
> +}
> +#endif /* CONFIG_CPU_THERMAL_HOTPLUG */
> +
> +#endif /* __CPU_COOLING_H__ */
> --
> 1.7.9.5
>


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