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 the frequency 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 queries the
host CPU frequency by reading a MMIO region of a virtual cpufreq device
to update the guest's frequency scaling factor periodically. This enables
accurate Per-Entity Load Tracking for tasks running in the guest.
Co-developed-by: Saravana Kannan <saravanak@xxxxxxxxxx>
Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
Signed-off-by: David Dai <davidai@xxxxxxxxxx>
---
drivers/cpufreq/Kconfig | 14 ++
drivers/cpufreq/Makefile | 1 +
drivers/cpufreq/virtual-cpufreq.c | 333 ++++++++++++++++++++++++++++++
include/linux/arch_topology.h | 1 +
4 files changed, 349 insertions(+)
create mode 100644 drivers/cpufreq/virtual-cpufreq.c
diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
index 2561b215432a..92a83a9bb2e1 100644
--- a/drivers/cpufreq/Kconfig
+++ b/drivers/cpufreq/Kconfig
@@ -217,6 +217,20 @@ config CPUFREQ_DT
If in doubt, say N.
+config CPUFREQ_VIRT
+ tristate "Virtual cpufreq driver"
+ depends on GENERIC_ARCH_TOPOLOGY
+ help
+ This adds a virtualized cpufreq driver for guest kernels that
+ read/writes to a MMIO region for a virtualized cpufreq device to
+ communicate with the host. It sends performance requests to the host
+ which gets used as a hint 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
tristate "Generic DT based cpufreq platdev driver"
depends on OF
diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
index 0f184031dd12..10d7d6e55da8 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_VIRT) += virtual-cpufreq.o
# Traces
CFLAGS_amd-pstate-trace.o := -I$(src)
diff --git a/drivers/cpufreq/virtual-cpufreq.c b/drivers/cpufreq/virtual-cpufreq.c
new file mode 100644
index 000000000000..a050b3a6737f
--- /dev/null
+++ b/drivers/cpufreq/virtual-cpufreq.c
@@ -0,0 +1,333 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 Google LLC
+ */
+
+#include <linux/arch_topology.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/platform_device.h>
+#include <linux/slab.h>
+
+/*
+ * CPU0..CPUn
+ * +-------------+-------------------------------+--------+-------+
+ * | Register | Description | Offset | Len |
+ * +-------------+-------------------------------+--------+-------+
+ * | cur_perf | read this register to get | 0x0 | 0x4 |
+ * | | the current perf (integer val | | |
+ * | | representing perf relative to | | |
+ * | | max performance) | | |
+ * | | that vCPU is running at | | |
+ * +-------------+-------------------------------+--------+-------+
+ * | set_perf | write to this register to set | 0x4 | 0x4 |
+ * | | perf value of the vCPU | | |
+ * +-------------+-------------------------------+--------+-------+
+ * | perftbl_len | number of entries in perf | 0x8 | 0x4 |
+ * | | table. A single entry in the | | |
+ * | | perf table denotes no table | | |
+ * | | and the entry contains | | |
+ * | | the maximum perf value | | |
+ * | | that this vCPU supports. | | |
+ * | | The guest can request any | | |
+ * | | value between 1 and max perf | | |
+ * | | when perftbls are not used. | | |
+ * +---------------------------------------------+--------+-------+
+ * | perftbl_sel | write to this register to | 0xc | 0x4 |
+ * | | select perf table entry to | | |
+ * | | read from | | |
+ * +---------------------------------------------+--------+-------+
+ * | perftbl_rd | read this register to get | 0x10 | 0x4 |
+ * | | perf value of the selected | | |
+ * | | entry based on perftbl_sel | | |
+ * +---------------------------------------------+--------+-------+
+ * | perf_domain | performance domain number | 0x14 | 0x4 |
+ * | | that this vCPU belongs to. | | |
+ * | | vCPUs sharing the same perf | | |
+ * | | domain number are part of the | | |
+ * | | same performance domain. | | |
+ * +-------------+-------------------------------+--------+-------+
+ */
+
+#define REG_CUR_PERF_STATE_OFFSET 0x0
+#define REG_SET_PERF_STATE_OFFSET 0x4
+#define REG_PERFTBL_LEN_OFFSET 0x8
+#define REG_PERFTBL_SEL_OFFSET 0xc
+#define REG_PERFTBL_RD_OFFSET 0x10
+#define REG_PERF_DOMAIN_OFFSET 0x14
+#define PER_CPU_OFFSET 0x1000
+
+#define PERFTBL_MAX_ENTRIES 64U
+
+static void __iomem *base;
+static DEFINE_PER_CPU(u32, perftbl_num_entries);
+
+static void virt_scale_freq_tick(void)
+{
+ int cpu = smp_processor_id();
+ u32 max_freq = (u32)cpufreq_get_hw_max_freq(cpu);
+ u64 cur_freq;
+ unsigned long scale;
+
+ cur_freq = (u64)readl_relaxed(base + cpu * PER_CPU_OFFSET
+ + REG_CUR_PERF_STATE_OFFSET);
+
+ cur_freq <<= SCHED_CAPACITY_SHIFT;
+ scale = (unsigned long)div_u64(cur_freq, max_freq);
+ scale = min(scale, SCHED_CAPACITY_SCALE);
+
+ this_cpu_write(arch_freq_scale, scale);
+}
+
+static struct scale_freq_data virt_sfd = {
+ .source = SCALE_FREQ_SOURCE_VIRT,
+ .set_freq_scale = virt_scale_freq_tick,
+};
+
+static unsigned int virt_cpufreq_set_perf(struct cpufreq_policy *policy,
+ unsigned int target_freq)
+{
+ writel_relaxed(target_freq,
+ base + policy->cpu * PER_CPU_OFFSET + REG_SET_PERF_STATE_OFFSET);
+ return 0;
+}
+
+static unsigned int virt_cpufreq_fast_switch(struct cpufreq_policy *policy,
+ unsigned int target_freq)
+{
+ virt_cpufreq_set_perf(policy, target_freq);
+ return target_freq;
+}
+
+static u32 virt_cpufreq_get_perftbl_entry(int cpu, u32 idx)
+{
+ writel_relaxed(idx, base + cpu * PER_CPU_OFFSET +
+ REG_PERFTBL_SEL_OFFSET);
+ return readl_relaxed(base + cpu * PER_CPU_OFFSET +
+ REG_PERFTBL_RD_OFFSET);
+}
+
+static int virt_cpufreq_target(struct cpufreq_policy *policy,
+ unsigned int target_freq,
+ unsigned int relation)
+{
+ struct cpufreq_freqs freqs;
+ int ret = 0;
+
+ freqs.old = policy->cur;
+ freqs.new = target_freq;
+
+ cpufreq_freq_transition_begin(policy, &freqs);
+ ret = virt_cpufreq_set_perf(policy, target_freq);
+ cpufreq_freq_transition_end(policy, &freqs, ret != 0);
+
+ return ret;
+}
+
+static int virt_cpufreq_get_sharing_cpus(struct cpufreq_policy *policy)
+{
+ u32 cur_perf_domain, perf_domain;
+ struct device *cpu_dev;
+ int cpu;
+
+ cur_perf_domain = readl_relaxed(base + policy->cpu *
+ PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET);
+
+ for_each_possible_cpu(cpu) {
+ cpu_dev = get_cpu_device(cpu);
+ if (!cpu_dev)
+ continue;
+
+ perf_domain = readl_relaxed(base + cpu *
+ PER_CPU_OFFSET + REG_PERF_DOMAIN_OFFSET);
+
+ if (perf_domain == cur_perf_domain)
+ cpumask_set_cpu(cpu, policy->cpus);
+ }
+
+ return 0;
+}
+
+static int virt_cpufreq_get_freq_info(struct cpufreq_policy *policy)
+{
+ struct cpufreq_frequency_table *table;
+ u32 num_perftbl_entries, idx;
+
+ num_perftbl_entries = per_cpu(perftbl_num_entries, policy->cpu);
+
+ if (num_perftbl_entries == 1) {
+ policy->cpuinfo.min_freq = 1;
+ policy->cpuinfo.max_freq = virt_cpufreq_get_perftbl_entry(policy->cpu, 0);
+
+ policy->min = policy->cpuinfo.min_freq;
+ policy->max = policy->cpuinfo.max_freq;
+
+ policy->cur = policy->max;
+ return 0;
+ }
+
+ table = kcalloc(num_perftbl_entries + 1, sizeof(*table), GFP_KERNEL);
+ if (!table)
+ return -ENOMEM;
+
+ for (idx = 0; idx < num_perftbl_entries; idx++)
+ table[idx].frequency = virt_cpufreq_get_perftbl_entry(policy->cpu, idx);
+
+ table[idx].frequency = CPUFREQ_TABLE_END;
+ policy->freq_table = table;
+
+ return 0;
+}
+
+static int virt_cpufreq_cpu_init(struct cpufreq_policy *policy)
+{
+ struct device *cpu_dev;
+ int ret;
+
+ cpu_dev = get_cpu_device(policy->cpu);
+ if (!cpu_dev)
+ return -ENODEV;
+
+ ret = virt_cpufreq_get_freq_info(policy);
+ if (ret) {
+ dev_warn(cpu_dev, "failed to get cpufreq info\n");
+ return ret;
+ }
+
+ ret = virt_cpufreq_get_sharing_cpus(policy);
+ if (ret) {
+ dev_warn(cpu_dev, "failed to get sharing cpumask\n");
+ return ret;
+ }
+
+ /*
+ * To simplify and improve latency of handling frequency requests on
+ * the host side, this ensures that the vCPU thread triggering the MMIO
+ * abort is the same thread whose performance constraints (Ex. uclamp
+ * settings) need to be updated. This simplifies the VMM (Virtual
+ * Machine Manager) having to find the correct vCPU thread and/or
+ * facing permission issues when configuring other threads.
+ */
+ policy->dvfs_possible_from_any_cpu = false;
+ policy->fast_switch_possible = true;
+
+ /*
+ * Using the default SCALE_FREQ_SOURCE_CPUFREQ is insufficient since
+ * the actual physical CPU frequency may not match requested frequency
+ * from the vCPU thread due to frequency update latencies or other
+ * inputs to the physical CPU frequency selection. This additional FIE
+ * source allows for more accurate freq_scale updates and only takes
+ * effect if another FIE source such as AMUs have not been registered.
+ */
+ topology_set_scale_freq_source(&virt_sfd, policy->cpus);
+
+ return 0;
+}
+
+static void virt_cpufreq_cpu_exit(struct cpufreq_policy *policy)
+{
+ topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_VIRT, policy->related_cpus);
+ kfree(policy->freq_table);
+}
+
+static int virt_cpufreq_online(struct cpufreq_policy *policy)
+{
+ /* Nothing to restore. */
+ return 0;
+}
+
+static int virt_cpufreq_offline(struct cpufreq_policy *policy)
+{
+ /* Dummy offline() to avoid exit() being called and freeing resources. */
+ return 0;
+}
+
+static int virt_cpufreq_verify_policy(struct cpufreq_policy_data *policy)
+{
+ if (policy->freq_table)
+ return cpufreq_frequency_table_verify(policy, policy->freq_table);
+
+ cpufreq_verify_within_cpu_limits(policy);
+ return 0;
+}
+
+static struct cpufreq_driver cpufreq_virt_driver = {
+ .name = "virt-cpufreq",
+ .init = virt_cpufreq_cpu_init,
+ .exit = virt_cpufreq_cpu_exit,
+ .online = virt_cpufreq_online,
+ .offline = virt_cpufreq_offline,
+ .verify = virt_cpufreq_verify_policy,
+ .target = virt_cpufreq_target,
+ .fast_switch = virt_cpufreq_fast_switch,
+ .attr = cpufreq_generic_attr,
+};
+
+static int virt_cpufreq_driver_probe(struct platform_device *pdev)
+{
+ u32 num_perftbl_entries;
+ int ret, cpu;
+
+ base = devm_platform_ioremap_resource(pdev, 0);
+ if (IS_ERR(base))
+ return PTR_ERR(base);
+
+ for_each_possible_cpu(cpu) {
+ num_perftbl_entries = readl_relaxed(base + cpu * PER_CPU_OFFSET +
+ REG_PERFTBL_LEN_OFFSET);
+
+ if (!num_perftbl_entries || num_perftbl_entries > PERFTBL_MAX_ENTRIES)
+ return -ENODEV;
+
+ per_cpu(perftbl_num_entries, cpu) = num_perftbl_entries;
+ }
+
+ ret = cpufreq_register_driver(&cpufreq_virt_driver);
+ if (ret) {
+ dev_err(&pdev->dev, "Virtual CPUFreq driver failed to register: %d\n", ret);
+ return ret;
+ }
+
+ dev_dbg(&pdev->dev, "Virtual CPUFreq driver initialized\n");
+ return 0;
+}
+
+static void virt_cpufreq_driver_remove(struct platform_device *pdev)
+{
+ cpufreq_unregister_driver(&cpufreq_virt_driver);
+}
+
+static const struct of_device_id virt_cpufreq_match[] = {
+ { .compatible = "qemu,virtual-cpufreq", .data = NULL},
+ {}
+};
+MODULE_DEVICE_TABLE(of, virt_cpufreq_match);
+
+static struct platform_driver virt_cpufreq_driver = {
+ .probe = virt_cpufreq_driver_probe,
+ .remove = virt_cpufreq_driver_remove,
+ .driver = {
+ .name = "virt-cpufreq",
+ .of_match_table = virt_cpufreq_match,
+ },
+};
+
+static int __init virt_cpufreq_init(void)
+{
+ return platform_driver_register(&virt_cpufreq_driver);
+}
+postcore_initcall(virt_cpufreq_init);
+
+static void __exit virt_cpufreq_exit(void)
+{
+ platform_driver_unregister(&virt_cpufreq_driver);
+}
+module_exit(virt_cpufreq_exit);
+
+MODULE_DESCRIPTION("Virtual cpufreq driver");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index b721f360d759..d5d848849408 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -49,6 +49,7 @@ enum scale_freq_source {
SCALE_FREQ_SOURCE_CPUFREQ = 0,
SCALE_FREQ_SOURCE_ARCH,
SCALE_FREQ_SOURCE_CPPC,
+ SCALE_FREQ_SOURCE_VIRT,
};
struct scale_freq_data {
--
2.46.0.792.g87dc391469-goog
