[RFC PATCH v2 6/6] cpufreq: add kvm-cpufreq driver
David Dai
davidai at google.com
Thu Mar 30 18:43:50 PDT 2023
Introduce a virtualized cpufreq driver for guest kernels to improve
performance and power of workloads within VMs.
This driver does two main things:
1. Sends utilization of vCPUs as a hint to the host. The host uses the
hint to schedule the vCPU threads and decide physical CPU frequency.
2. If a VM does not support a virtualized FIE(like AMUs), it uses
hypercalls to update the guest's frequency scaling factor periodically
by querying the host CPU frequency. This enables accurate
Per-Entity Load Tracking for tasks running in the guest.
Note that because the host already employs a rate_limit_us, we set the
transition_delay_us of the cpufreq policy to a miniscule value(1)
to avoid any additional delays between when the runqueue's util change
and a frequency response on the host.
Co-developed-by: Saravana Kannan <saravanak at google.com>
Signed-off-by: Saravana Kannan <saravanak at google.com>
Signed-off-by: David Dai <davidai at google.com>
---
drivers/cpufreq/Kconfig | 13 ++
drivers/cpufreq/Makefile | 1 +
drivers/cpufreq/kvm-cpufreq.c | 245 ++++++++++++++++++++++++++++++++++
include/linux/sched.h | 1 +
kernel/sched/core.c | 6 +
5 files changed, 266 insertions(+)
create mode 100644 drivers/cpufreq/kvm-cpufreq.c
diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
index 2c839bd2b051..0ef9d5be7c4d 100644
--- a/drivers/cpufreq/Kconfig
+++ b/drivers/cpufreq/Kconfig
@@ -217,6 +217,19 @@ config CPUFREQ_DT
If in doubt, say N.
+config CPUFREQ_KVM
+ tristate "KVM cpufreq driver"
+ help
+ This adds a virtualized KVM cpufreq driver for guest kernels that
+ uses hypercalls to communicate with the host. It sends utilization
+ updates to the host and gets used to schedule vCPU threads and
+ select CPU frequency. If a VM does not support a virtualized FIE
+ such as AMUs, it updates the frequency scaling factor by polling
+ host CPU frequency to enable accurate Per-Entity Load Tracking
+ for tasks running in the guest.
+
+ If in doubt, say N.
+
config CPUFREQ_DT_PLATDEV
bool
help
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index ef8510774913..179ea8d45135 100644
--- a/drivers/cpufreq/Makefile
+++ b/drivers/cpufreq/Makefile
@@ -16,6 +16,7 @@ obj-$(CONFIG_CPU_FREQ_GOV_ATTR_SET) += cpufreq_governor_attr_set.o
obj-$(CONFIG_CPUFREQ_DT) += cpufreq-dt.o
obj-$(CONFIG_CPUFREQ_DT_PLATDEV) += cpufreq-dt-platdev.o
+obj-$(CONFIG_CPUFREQ_KVM) += kvm-cpufreq.o
# Traces
CFLAGS_amd-pstate-trace.o := -I$(src)
diff --git a/drivers/cpufreq/kvm-cpufreq.c b/drivers/cpufreq/kvm-cpufreq.c
new file mode 100644
index 000000000000..1542c9ac4119
--- /dev/null
+++ b/drivers/cpufreq/kvm-cpufreq.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Google LLC
+ */
+
+#include <linux/arch_topology.h>
+#include <linux/arm-smccc.h>
+#include <linux/cpufreq.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+#include <linux/pm_opp.h>
+#include <linux/slab.h>
+
+static void kvm_scale_freq_tick(void)
+{
+ unsigned long scale, cur_freq, max_freq;
+ struct arm_smccc_res hvc_res;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_GET_CUR_CPUFREQ_FUNC_ID,
+ 0, &hvc_res);
+
+ cur_freq = hvc_res.a0;
+ max_freq = cpufreq_get_hw_max_freq(task_cpu(current));
+ scale = (cur_freq << SCHED_CAPACITY_SHIFT) / max_freq;
+
+ this_cpu_write(arch_freq_scale, (unsigned long)scale);
+}
+
+static struct scale_freq_data kvm_sfd = {
+ .source = SCALE_FREQ_SOURCE_ARCH,
+ .set_freq_scale = kvm_scale_freq_tick,
+};
+
+struct remote_data {
+ int ret;
+ struct cpufreq_frequency_table *table;
+};
+
+static void remote_get_freqtbl_num_entries(void *data)
+{
+ struct arm_smccc_res hvc_res;
+ u32 freq = 1UL;
+ int *idx = data;
+
+ while (freq != CPUFREQ_TABLE_END) {
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_GET_CPUFREQ_TBL_FUNC_ID,
+ *idx, &hvc_res);
+ if (hvc_res.a0) {
+ *idx = -ENODEV;
+ return;
+ }
+ freq = hvc_res.a1;
+ (*idx)++;
+ }
+}
+
+static int kvm_cpufreq_get_freqtbl_num_entries(int cpu)
+{
+ int num_entries = 0;
+
+ smp_call_function_single(cpu, remote_get_freqtbl_num_entries, &num_entries, true);
+ return num_entries;
+}
+
+static void remote_populate_freqtbl(void *data)
+{
+ struct arm_smccc_res hvc_res;
+ struct remote_data *freq_data = data;
+ struct cpufreq_frequency_table *pos;
+ struct cpufreq_frequency_table *table = freq_data->table;
+ int idx;
+
+ cpufreq_for_each_entry_idx(pos, table, idx) {
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_GET_CPUFREQ_TBL_FUNC_ID,
+ idx, &hvc_res);
+ if (hvc_res.a0) {
+ freq_data->ret = -ENODEV;
+ return;
+ }
+ pos->frequency = hvc_res.a1;
+ }
+ freq_data->ret = 0;
+}
+
+static int kvm_cpufreq_populate_freqtbl(struct cpufreq_frequency_table *table, int cpu)
+{
+ struct remote_data freq_data;
+
+ freq_data.table = table;
+ smp_call_function_single(cpu, remote_populate_freqtbl, &freq_data, true);
+ return freq_data.ret;
+}
+
+static unsigned int kvm_cpufreq_setutil_hyp(struct cpufreq_policy *policy)
+{
+ struct arm_smccc_res hvc_res;
+ u32 util = sched_cpu_util_freq(policy->cpu);
+ u32 cap = arch_scale_cpu_capacity(policy->cpu);
+ u32 threshold = cap - (cap >> 2);
+
+ if (util > threshold)
+ util = (cap + threshold) >> 1;
+
+ arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_KVM_UTIL_HINT_FUNC_ID,
+ util, &hvc_res);
+
+ return hvc_res.a0;
+}
+
+static unsigned int kvm_cpufreq_fast_switch(struct cpufreq_policy *policy,
+ unsigned int target_freq)
+{
+ kvm_cpufreq_setutil_hyp(policy);
+ return target_freq;
+}
+
+static int kvm_cpufreq_target_index(struct cpufreq_policy *policy,
+ unsigned int index)
+{
+ return kvm_cpufreq_setutil_hyp(policy);
+}
+
+static const struct of_device_id kvm_cpufreq_match[] = {
+ { .compatible = "virtual,kvm-cpufreq"},
+ {}
+};
+MODULE_DEVICE_TABLE(of, kvm_cpufreq_match);
+
+static int kvm_cpufreq_cpu_init(struct cpufreq_policy *policy)
+{
+ struct device *cpu_dev;
+ struct cpufreq_frequency_table *table;
+ int num_entries;
+
+ cpu_dev = get_cpu_device(policy->cpu);
+ if (!cpu_dev) {
+ pr_err("%s: failed to get cpu%d device\n", __func__,
+ policy->cpu);
+ return -ENODEV;
+ }
+
+ num_entries = kvm_cpufreq_get_freqtbl_num_entries(policy->cpu);
+ if (num_entries == -ENODEV)
+ return -ENODEV;
+
+ table = kcalloc(num_entries, sizeof(*table), GFP_KERNEL);
+ if (!table)
+ return -ENOMEM;
+
+ table[num_entries-1].frequency = CPUFREQ_TABLE_END;
+
+ if (kvm_cpufreq_populate_freqtbl(table, policy->cpu))
+ return -ENODEV;
+
+ policy->freq_table = table;
+ policy->dvfs_possible_from_any_cpu = false;
+ policy->fast_switch_possible = true;
+ policy->transition_delay_us = 1;
+
+ /*
+ * Only takes effect if another FIE source such as AMUs
+ * have not been registered.
+ */
+ topology_set_scale_freq_source(&kvm_sfd, policy->cpus);
+
+ return 0;
+}
+
+static int kvm_cpufreq_cpu_exit(struct cpufreq_policy *policy)
+{
+ kfree(policy->freq_table);
+ return 0;
+}
+
+static int kvm_cpufreq_online(struct cpufreq_policy *policy)
+{
+ /* Nothing to restore. */
+ return 0;
+}
+
+static int kvm_cpufreq_offline(struct cpufreq_policy *policy)
+{
+ /* Dummy offline() to avoid exit() being called and freeing resources. */
+ return 0;
+}
+
+static struct cpufreq_driver cpufreq_kvm_driver = {
+ .name = "kvm-cpufreq",
+ .init = kvm_cpufreq_cpu_init,
+ .exit = kvm_cpufreq_cpu_exit,
+ .online = kvm_cpufreq_online,
+ .offline = kvm_cpufreq_offline,
+ .verify = cpufreq_generic_frequency_table_verify,
+ .target_index = kvm_cpufreq_target_index,
+ .fast_switch = kvm_cpufreq_fast_switch,
+ .attr = cpufreq_generic_attr,
+};
+
+static int kvm_cpufreq_driver_probe(struct platform_device *pdev)
+{
+ int ret;
+
+ ret = cpufreq_register_driver(&cpufreq_kvm_driver);
+ if (ret) {
+ dev_err(&pdev->dev, "KVM CPUFreq driver failed to register: %d\n", ret);
+ return ret;
+ }
+
+ dev_dbg(&pdev->dev, "KVM CPUFreq driver initialized\n");
+ return 0;
+}
+
+static int kvm_cpufreq_driver_remove(struct platform_device *pdev)
+{
+ cpufreq_unregister_driver(&cpufreq_kvm_driver);
+ return 0;
+}
+
+static struct platform_driver kvm_cpufreq_driver = {
+ .probe = kvm_cpufreq_driver_probe,
+ .remove = kvm_cpufreq_driver_remove,
+ .driver = {
+ .name = "kvm-cpufreq",
+ .of_match_table = kvm_cpufreq_match,
+ },
+};
+
+static int __init kvm_cpufreq_init(void)
+{
+ return platform_driver_register(&kvm_cpufreq_driver);
+}
+postcore_initcall(kvm_cpufreq_init);
+
+static void __exit kvm_cpufreq_exit(void)
+{
+ platform_driver_unregister(&kvm_cpufreq_driver);
+}
+module_exit(kvm_cpufreq_exit);
+
+MODULE_DESCRIPTION("KVM cpufreq driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d8c346fcdf52..bd38aa32a57c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2303,6 +2303,7 @@ static inline bool owner_on_cpu(struct task_struct *owner)
/* Returns effective CPU energy utilization, as seen by the scheduler */
unsigned long sched_cpu_util(int cpu);
+unsigned long sched_cpu_util_freq(int cpu);
#endif /* CONFIG_SMP */
#ifdef CONFIG_RSEQ
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7700ef5610c1..dd46f4cc629b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7421,6 +7421,12 @@ unsigned long sched_cpu_util(int cpu)
{
return effective_cpu_util(cpu, cpu_util_cfs(cpu), ENERGY_UTIL, NULL);
}
+
+unsigned long sched_cpu_util_freq(int cpu)
+{
+ return effective_cpu_util(cpu, cpu_util_cfs(cpu), FREQUENCY_UTIL, NULL);
+}
+
#endif /* CONFIG_SMP */
/**
--
2.40.0.348.gf938b09366-goog
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