Hi Thomas, Peter,
as per commit log, with this patch Kevin is adding a PSCI firmware
checker to the kernel. As a bit of background, the PSCI firmware
interface is used on ARM to enter idle states and to power off
a CPU, similar to mwait on x86 (at least for idle states).
I asked Kevin to copy you in since, to test the PSCI suspend
interface we kind of mirror what eg x86 PowerClamp did in the past
(well, what it currently does too :)) to let a core go idle (high
priority thread that just sets a timer and call the PSCI suspend method
ie mwait in ARM world) and since I am aware that created all sorts of
issues/flames when powerclamp was merged I wanted to check with you if
the approach we took (which is similar to powerclamp but should be a bit
more lightweight) is sound, last thing we want is abusing the tick/sched
API to implement a checker so we are asking.
There are some niggles to fix (tick broadcast enter/exit usage on
systems with no HW broadcast timer, we can't suspend on one core
owning the hrtimer soft broadcast, but that's not different from
CPUidle), but it is more to have your comment on the whole approach
when/if you have time to have a look, much appreciated.
Thanks a lot !
Lorenzo
On Tue, Aug 16, 2016 at 11:34:06AM +0100, Kevin Brodsky wrote:
> Add a PSCI checker module that enables basic testing of PSCI
> operations during startup. There are two main tests: CPU hotplugging
> and suspending.
>
> In the hotplug tests, the hotplug API is used to turn off and on again
> all CPUs in the system, and then all CPUs in each cluster, checking
> the consistency of the return codes.
>
> In the suspend tests, a high-priority thread is created on each core
> and uses low-level cpuidle functionalities to enter suspend, in all
> the possible states and multiple times. This should allow a maximum
> number of CPUs to enter the same sleep state at the same or slightly
> different time.
>
> While in theory power management PSCI functions (CPU_{ON,OFF,SUSPEND})
> could be directly called, this proved too difficult as it would imply
> the duplication of all the logic used by the kernel to allow for a
> clean shutdown/bringup/suspend of the CPU (the deepest sleep states
> implying potentially the shutdown of the CPU).
>
> Note that the module cannot be compiled as a loadable module, since it
> uses a number of non-exported identifiers (essentially for
> PSCI-specific checks and direct use of cpuidle) and relies on the
> absence of userspace to avoid races when calling hotplug and cpuidle
> functions.
>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Sudeep Holla <sudeep.holla@xxxxxxx>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
> ---
> drivers/firmware/Kconfig | 7 +
> drivers/firmware/Makefile | 1 +
> drivers/firmware/psci_checker.c | 484 ++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 492 insertions(+)
> create mode 100644 drivers/firmware/psci_checker.c
>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index 0e22f241403b..0033c8755104 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -206,6 +206,13 @@ config QCOM_SCM_64
> config HAVE_ARM_SMCCC
> bool
>
> +config PSCI_CHECKER
> + bool "PSCI checker"
> + depends on ARM_PSCI_FW && HOTPLUG_CPU
> + help
> + Run the PSCI checker during startup. This checks that hotplug and
> + suspend operations work correctly when using PSCI.
> +
> source "drivers/firmware/broadcom/Kconfig"
> source "drivers/firmware/google/Kconfig"
> source "drivers/firmware/efi/Kconfig"
> diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
> index 44a59dcfc398..3efc794906c6 100644
> --- a/drivers/firmware/Makefile
> +++ b/drivers/firmware/Makefile
> @@ -20,6 +20,7 @@ obj-$(CONFIG_QCOM_SCM) += qcom_scm.o
> obj-$(CONFIG_QCOM_SCM_64) += qcom_scm-64.o
> obj-$(CONFIG_QCOM_SCM_32) += qcom_scm-32.o
> CFLAGS_qcom_scm-32.o :=$(call as-instr,.arch armv7-a\n.arch_extension sec,-DREQUIRES_SEC=1) -march=armv7-a
> +obj-$(CONFIG_PSCI_CHECKER) += psci_checker.o
>
> obj-y += broadcom/
> obj-$(CONFIG_GOOGLE_FIRMWARE) += google/
> diff --git a/drivers/firmware/psci_checker.c b/drivers/firmware/psci_checker.c
> new file mode 100644
> index 000000000000..b2768f2a3919
> --- /dev/null
> +++ b/drivers/firmware/psci_checker.c
> @@ -0,0 +1,484 @@
> +/*
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * 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.
> + *
> + * Copyright (C) 2016 ARM Limited
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/atomic.h>
> +#include <linux/completion.h>
> +#include <linux/cpu.h>
> +#include <linux/cpuidle.h>
> +#include <linux/cpu_pm.h>
> +#include <linux/kernel.h>
> +#include <linux/kthread.h>
> +#include <linux/module.h>
> +#include <linux/preempt.h>
> +#include <linux/psci.h>
> +#include <linux/slab.h>
> +#include <linux/tick.h>
> +#include <linux/topology.h>
> +
> +#include <asm/cpuidle.h>
> +
> +#include <uapi/linux/psci.h>
> +
> +#define NUM_SUSPEND_CYCLE (10)
> +
> +static unsigned int nb_available_cpus;
> +static int tos_resident_cpu = -1;
> +
> +static atomic_t nb_active_threads;
> +static struct completion suspend_threads_started =
> + COMPLETION_INITIALIZER(suspend_threads_started);
> +static struct completion suspend_threads_done =
> + COMPLETION_INITIALIZER(suspend_threads_done);
> +
> +/*
> + * We assume that PSCI operations are used if they are available. This is not
> + * necessarily true on arm64, since the decision is based on the
> + * "enable-method" property of each CPU in the DT, but given that there is no
> + * arch-specific way to check this, we assume that the DT is sensible.
> + */
> +static int psci_ops_check(void)
> +{
> + int migrate_type = -1;
> + int cpu;
> +
> + if (!(psci_ops.cpu_off && psci_ops.cpu_on && psci_ops.cpu_suspend)) {
> + pr_warn("Missing PSCI operations, aborting tests\n");
> + return -EOPNOTSUPP;
> + }
> +
> + if (psci_ops.migrate_info_type)
> + migrate_type = psci_ops.migrate_info_type();
> +
> + if (migrate_type == PSCI_0_2_TOS_UP_MIGRATE ||
> + migrate_type == PSCI_0_2_TOS_UP_NO_MIGRATE) {
> + /* There is a UP Trusted OS, find on which core it resides. */
> + for_each_online_cpu(cpu)
> + if (psci_tos_resident_on(cpu)) {
> + tos_resident_cpu = cpu;
> + break;
> + }
> + if (tos_resident_cpu == -1)
> + pr_warn("UP Trusted OS resides on no online CPU\n");
> + }
> +
> + return 0;
> +}
> +
> +static int find_clusters(const struct cpumask *cpus,
> + const struct cpumask **clusters)
> +{
> + unsigned int nb = 0;
> + cpumask_var_t tmp;
> +
> + if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
> + return -ENOMEM;
> + cpumask_copy(tmp, cpus);
> +
> + while (!cpumask_empty(tmp)) {
> + const struct cpumask *cluster =
> + topology_core_cpumask(cpumask_any(tmp));
> +
> + clusters[nb++] = cluster;
> + cpumask_andnot(tmp, tmp, cluster);
> + }
> +
> + free_cpumask_var(tmp);
> + return nb;
> +}
> +
> +/*
> + * offlined_cpus is a temporary array but passing it as an argument avoids
> + * multiple allocations.
> + */
> +static unsigned int down_and_up_cpus(const struct cpumask *cpus,
> + struct cpumask *offlined_cpus)
> +{
> + int cpu;
> + int err = 0;
> +
> + cpumask_clear(offlined_cpus);
> +
> + /* Try to power down all CPUs in the mask. */
> + for_each_cpu(cpu, cpus) {
> + int ret = cpu_down(cpu);
> +
> + /*
> + * cpu_down() checks the number of online CPUs before the TOS
> + * resident CPU.
> + */
> + if (cpumask_weight(offlined_cpus) + 1 == nb_available_cpus) {
> + if (ret != -EBUSY) {
> + pr_err("Unexpected return code %d while trying "
> + "to power down last online CPU %d\n",
> + ret, cpu);
> + ++err;
> + }
> + } else if (cpu == tos_resident_cpu) {
> + if (ret != -EPERM) {
> + pr_err("Unexpected return code %d while trying "
> + "to power down TOS resident CPU %d\n",
> + ret, cpu);
> + ++err;
> + }
> + } else if (ret != 0) {
> + pr_err("Error occurred (%d) while trying "
> + "to power down CPU %d\n", ret, cpu);
> + ++err;
> + }
> +
> + if (ret == 0)
> + cpumask_set_cpu(cpu, offlined_cpus);
> + }
> +
> + /* Try to power up all the CPUs that have been offlined. */
> + for_each_cpu(cpu, offlined_cpus) {
> + int ret = cpu_up(cpu);
> +
> + if (ret != 0) {
> + pr_err("Error occurred (%d) while trying "
> + "to power up CPU %d\n", ret, cpu);
> + ++err;
> + } else {
> + cpumask_clear_cpu(cpu, offlined_cpus);
> + }
> + }
> +
> + /*
> + * Something went bad at some point and some CPUs could not be turned
> + * back on.
> + */
> + WARN_ON(!cpumask_empty(offlined_cpus) ||
> + num_online_cpus() != nb_available_cpus);
> +
> + return err;
> +}
> +
> +static int hotplug_tests(void)
> +{
> + int err;
> + cpumask_var_t offlined_cpus;
> + int i, nb_cluster;
> + const struct cpumask **clusters;
> + char *page_buf;
> +
> + err = -ENOMEM;
> + if (!alloc_cpumask_var(&offlined_cpus, GFP_KERNEL))
> + return err;
> + /* We may have up to nb_available_cpus clusters. */
> + clusters = kmalloc_array(nb_available_cpus, sizeof(*clusters),
> + GFP_KERNEL);
> + if (!clusters)
> + goto out_free_cpus;
> + page_buf = (char *)__get_free_page(GFP_KERNEL);
> + if (!page_buf)
> + goto out_free_clusters;
> +
> + err = 0;
> + nb_cluster = find_clusters(cpu_online_mask, clusters);
> +
> + /*
> + * Of course the last CPU cannot be powered down and cpu_down() should
> + * refuse doing that.
> + */
> + pr_info("Trying to turn off and on again all CPUs\n");
> + err += down_and_up_cpus(cpu_online_mask, offlined_cpus);
> +
> + /*
> + * Take down CPUs by cluster this time. When the last CPU is turned
> + * off, the cluster itself should shut down.
> + */
> + for (i = 0; i < nb_cluster; ++i) {
> + int cluster_id =
> + topology_physical_package_id(cpumask_any(clusters[i]));
> + ssize_t len = cpumap_print_to_pagebuf(true, page_buf,
> + clusters[i]);
> + /* Remove trailing newline. */
> + page_buf[len - 1] = '\0';
> + pr_info("Trying to turn off and on again cluster %d "
> + "(CPUs %s)\n", cluster_id, page_buf);
> + err += down_and_up_cpus(clusters[i], offlined_cpus);
> + }
> +
> + free_page((unsigned long)page_buf);
> +out_free_clusters:
> + kfree(clusters);
> +out_free_cpus:
> + free_cpumask_var(offlined_cpus);
> + return err;
> +}
> +
> +static void dummy_callback(unsigned long ignored) {}
> +
> +static int suspend_cpu(int index, bool broadcast)
> +{
> + int ret;
> +
> + arch_cpu_idle_enter();
> +
> + if (broadcast) {
> + /*
> + * The local timer will be shut down, we need to enter tick
> + * broadcast. This will fail if the CPU is used to broadcast
> + * wakeups.
> + */
> + ret = tick_broadcast_enter();
> + if (ret)
> + goto out_arch_exit;
> + }
> +
> + /*
> + * Replicate the common ARM cpuidle enter function
> + * (arm_enter_idle_state).
> + */
> + ret = CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, index);
> +
> + if (broadcast)
> + tick_broadcast_exit();
> +
> +out_arch_exit:
> + arch_cpu_idle_exit();
> +
> + return ret;
> +}
> +
> +static int suspend_stress_thread(void *arg)
> +{
> + int cpu = (long)arg;
> + int i, err = 0;
> + struct sched_param sched_priority = { .sched_priority = MAX_RT_PRIO-1 };
> + struct cpuidle_device *dev;
> + struct cpuidle_driver *drv;
> + /* No need for an actual callback, we just want to wake up the CPU. */
> + struct timer_list wakeup_timer =
> + TIMER_INITIALIZER(dummy_callback, 0, 0);
> +
> + /* Wait for the main thread to give the start signal. */
> + wait_for_completion(&suspend_threads_started);
> +
> + /* Set maximum priority to preempt all other threads on this CPU. */
> + if (sched_setscheduler_nocheck(current, SCHED_FIFO, &sched_priority))
> + pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
> + cpu);
> +
> + dev = this_cpu_read(cpuidle_devices);
> + drv = cpuidle_get_cpu_driver(dev);
> +
> + pr_info("CPU %d entering suspend cycles, states 1 through %d\n",
> + cpu, drv->state_count - 1);
> +
> + for (i = 0; i < NUM_SUSPEND_CYCLE; ++i) {
> + int index;
> + /*
> + * Test all possible states, except 0 (which is usually WFI and
> + * doesn't use PSCI).
> + */
> + for (index = 1; index < drv->state_count; ++index) {
> + struct cpuidle_state *state = &drv->states[index];
> + bool broadcast = state->flags & CPUIDLE_FLAG_TIMER_STOP;
> + int ret;
> +
> + /*
> + * Set the timer to wake this CPU up in some time (which
> + * should be largely sufficient for entering suspend).
> + * If the local tick is disabled when entering suspend,
> + * suspend_cpu() takes care of switching to a broadcast
> + * tick, so the timer will still wake us up.
> + */
> + mod_timer(&wakeup_timer, jiffies + HZ *
> + state->target_residency / 1000000);
> +
> + /* IRQs must be disabled during suspend operations. */
> + local_irq_disable();
> +
> + ret = suspend_cpu(index, broadcast);
> +
> + /*
> + * We have woken up. Re-enable IRQs to handle any
> + * pending interrupt, do not wait until the end of the
> + * loop.
> + */
> + local_irq_enable();
> +
> + /*
> + * We expect to have entered the required state. Don't
> + * print a message if successful to avoid printing too
> + * many messages.
> + */
> + if (ret == index)
> + continue;
> +
> + if (ret >= 0)
> + pr_err("CPU %d resumed from unexpected state "
> + "%d (requested state %d, cycle %d)\n",
> + cpu, ret, index, i);
> + else
> + pr_err("Failed to suspend CPU %d: error %d "
> + "(requested state %d, cycle %d)\n",
> + cpu, ret, index, i);
> + ++err;
> + }
> + }
> +
> + /*
> + * Disable the timer to make sure that the timer will not trigger
> + * later.
> + */
> + del_timer(&wakeup_timer);
> +
> + if (atomic_dec_return_relaxed(&nb_active_threads) == 0)
> + complete(&suspend_threads_done);
> +
> + /* Give up on RT scheduling and wait for termination. */
> + sched_priority.sched_priority = 0;
> + if (sched_setscheduler_nocheck(current, SCHED_NORMAL, &sched_priority))
> + pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
> + cpu);
> + for (;;) {
> + /* Needs to be set first to avoid missing a wakeup. */
> + set_current_state(TASK_INTERRUPTIBLE);
> + if (kthread_should_stop()) {
> + __set_current_state(TASK_RUNNING);
> + break;
> + }
> + schedule();
> + }
> +
> + return err;
> +}
> +
> +static int suspend_tests(void)
> +{
> + int err = 0;
> + int i;
> + int cpu;
> + struct task_struct **threads;
> + int nb_threads = 0;
> +
> + threads = kmalloc_array(nb_available_cpus, sizeof(*threads),
> + GFP_KERNEL);
> + if (!threads)
> + return -ENOMEM;
> +
> + for_each_online_cpu(cpu) {
> + struct task_struct *thread;
> + /* Check that cpuidle is available on that CPU. */
> + struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
> + struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> +
> + if (cpuidle_not_available(drv, dev)) {
> + pr_warn("cpuidle not available on CPU %d, ignoring\n",
> + cpu);
> + continue;
> + }
> +
> + thread = kthread_create_on_cpu(suspend_stress_thread,
> + (void *)(long)cpu, cpu,
> + "psci_suspend_stress");
> + if (IS_ERR(thread))
> + pr_err("Failed to create kthread on CPU %d\n", cpu);
> + else
> + threads[nb_threads++] = thread;
> + }
> + if (nb_threads < 1) {
> + kfree(threads);
> + return -ENODEV;
> + }
> +
> + atomic_set(&nb_active_threads, nb_threads);
> +
> + /*
> + * Stop cpuidle to prevent the idle tasks from entering a deep sleep
> + * mode, as it might interfere with the suspend threads on other CPUs.
> + * This does not prevent the suspend threads from using cpuidle (only
> + * the idle tasks check for this status.
> + */
> + cpuidle_pause();
> +
> + /*
> + * Unpark the suspend threads. To avoid the main thread being preempted
> + * before all the threads have been unparked, the suspend threads will
> + * wait for the completion of suspend_threads_started.
> + */
> + for (i = 0; i < nb_threads; ++i)
> + kthread_unpark(threads[i]);
> + complete_all(&suspend_threads_started);
> +
> + wait_for_completion(&suspend_threads_done);
> +
> + cpuidle_resume();
> +
> + /* Stop and destroy all threads, get return status. */
> + for (i = 0; i < nb_threads; ++i) {
> + int ret = kthread_stop(threads[i]);
> + err += ret;
> + }
> +
> + kfree(threads);
> + return err;
> +}
> +
> +static int __init psci_checker(void)
> +{
> + int ret;
> +
> + /*
> + * Since we're in an initcall, we assume that all the CPUs that all
> + * CPUs that can be onlined have been onlined.
> + *
> + * The tests assume that hotplug is enabled but nobody else is using it,
> + * otherwise the results will be unpredictable. However, since there
> + * is no userspace yet in initcalls, that should be fine.
> + */
> + nb_available_cpus = num_online_cpus();
> +
> + /* Check PSCI operations are set up and working. */
> + ret = psci_ops_check();
> + if (ret)
> + return ret;
> +
> + pr_info("PSCI checker started using %u CPUs\n", nb_available_cpus);
> +
> + pr_info("Starting hotplug tests\n");
> + ret = hotplug_tests();
> + if (ret == 0)
> + pr_info("Hotplug tests passed OK\n");
> + else if (ret > 0)
> + pr_err("%d error(s) encountered in hotplug tests\n", ret);
> + else {
> + pr_err("Out of memory\n");
> + return ret;
> + }
> +
> + pr_info("Starting suspend tests\n");
> + ret = suspend_tests();
> + if (ret == 0)
> + pr_info("Suspend tests passed OK\n");
> + else if (ret > 0)
> + pr_err("%d error(s) encountered in suspend tests\n", ret);
> + else {
> + switch (ret) {
> + case -ENOMEM:
> + pr_err("Out of memory\n");
> + break;
> + case -ENODEV:
> + pr_warn("Could not start suspend tests on any CPU\n");
> + break;
> + }
> + }
> +
> + pr_info("PSCI checker completed\n");
> + return ret < 0 ? ret : 0;
> +}
> +late_initcall(psci_checker);
> --
> 2.9.2
>
