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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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dd52551fb7
Before commit 1328edca4a14 ("cpuidle-haltpoll: Enable kvm guest polling
when dedicated physical CPUs are available") the cpuidle-haltpoll driver
could also be used in scenarios when the host does not advertise the
KVM_HINTS_REALTIME hint.
While the behavior introduced by the aforementioned commit makes sense as
the default there are cases where the old behavior is desired, for example,
when other kernel changes triggered by presence by this hint are unwanted,
for some workloads where the latency benefit from polling overweights the
loss from idle CPU capacity that otherwise would be available, or just when
running under older Qemu versions that lack this hint.
Let's provide a typical "force" module parameter that allows restoring the
old behavior.
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
147 lines
3.1 KiB
C
147 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* cpuidle driver for haltpoll governor.
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*
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* Copyright 2019 Red Hat, Inc. and/or its affiliates.
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Authors: Marcelo Tosatti <mtosatti@redhat.com>
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*/
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#include <linux/init.h>
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#include <linux/cpu.h>
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#include <linux/cpuidle.h>
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#include <linux/module.h>
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#include <linux/sched/idle.h>
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#include <linux/kvm_para.h>
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#include <linux/cpuidle_haltpoll.h>
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static bool force __read_mostly;
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module_param(force, bool, 0444);
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MODULE_PARM_DESC(force, "Load unconditionally");
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static struct cpuidle_device __percpu *haltpoll_cpuidle_devices;
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static enum cpuhp_state haltpoll_hp_state;
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static int default_enter_idle(struct cpuidle_device *dev,
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struct cpuidle_driver *drv, int index)
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{
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if (current_clr_polling_and_test()) {
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local_irq_enable();
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return index;
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}
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default_idle();
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return index;
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}
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static struct cpuidle_driver haltpoll_driver = {
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.name = "haltpoll",
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.governor = "haltpoll",
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.states = {
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{ /* entry 0 is for polling */ },
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{
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.enter = default_enter_idle,
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.exit_latency = 1,
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.target_residency = 1,
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.power_usage = -1,
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.name = "haltpoll idle",
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.desc = "default architecture idle",
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},
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},
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.safe_state_index = 0,
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.state_count = 2,
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};
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static int haltpoll_cpu_online(unsigned int cpu)
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{
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struct cpuidle_device *dev;
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dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
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if (!dev->registered) {
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dev->cpu = cpu;
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if (cpuidle_register_device(dev)) {
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pr_notice("cpuidle_register_device %d failed!\n", cpu);
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return -EIO;
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}
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arch_haltpoll_enable(cpu);
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}
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return 0;
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}
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static int haltpoll_cpu_offline(unsigned int cpu)
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{
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struct cpuidle_device *dev;
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dev = per_cpu_ptr(haltpoll_cpuidle_devices, cpu);
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if (dev->registered) {
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arch_haltpoll_disable(cpu);
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cpuidle_unregister_device(dev);
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}
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return 0;
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}
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static void haltpoll_uninit(void)
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{
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if (haltpoll_hp_state)
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cpuhp_remove_state(haltpoll_hp_state);
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cpuidle_unregister_driver(&haltpoll_driver);
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free_percpu(haltpoll_cpuidle_devices);
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haltpoll_cpuidle_devices = NULL;
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}
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static bool haltpool_want(void)
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{
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return kvm_para_has_hint(KVM_HINTS_REALTIME) || force;
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}
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static int __init haltpoll_init(void)
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{
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int ret;
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struct cpuidle_driver *drv = &haltpoll_driver;
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/* Do not load haltpoll if idle= is passed */
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if (boot_option_idle_override != IDLE_NO_OVERRIDE)
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return -ENODEV;
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cpuidle_poll_state_init(drv);
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if (!kvm_para_available() || !haltpool_want())
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return -ENODEV;
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ret = cpuidle_register_driver(drv);
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if (ret < 0)
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return ret;
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haltpoll_cpuidle_devices = alloc_percpu(struct cpuidle_device);
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if (haltpoll_cpuidle_devices == NULL) {
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cpuidle_unregister_driver(drv);
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return -ENOMEM;
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}
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ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "cpuidle/haltpoll:online",
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haltpoll_cpu_online, haltpoll_cpu_offline);
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if (ret < 0) {
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haltpoll_uninit();
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} else {
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haltpoll_hp_state = ret;
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ret = 0;
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}
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return ret;
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}
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static void __exit haltpoll_exit(void)
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{
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haltpoll_uninit();
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}
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module_init(haltpoll_init);
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module_exit(haltpoll_exit);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Marcelo Tosatti <mtosatti@redhat.com>");
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