Hi folks,
Gentle nudge on this patch to see if there's any remaining concerns?
Thanks,
David
On Mon, May 20, 2024 at 10:32 PM David Dai <davidai@xxxxxxxxxx> wrote:
>
> 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 | 335 ++++++++++++++++++++++++++++++
> include/linux/arch_topology.h | 1 +
> 4 files changed, 351 insertions(+)
> create mode 100644 drivers/cpufreq/virtual-cpufreq.c
>
> diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
> index 94e55c40970a..9aa86bec5793 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 OF && 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 8d141c71b016..eb72ecdc24db 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..59ce2bda3913
> --- /dev/null
> +++ b/drivers/cpufreq/virtual-cpufreq.c
> @@ -0,0 +1,335 @@
> +// 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 int virt_cpufreq_cpu_exit(struct cpufreq_policy *policy)
> +{
> + topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_VIRT, policy->related_cpus);
> + kfree(policy->freq_table);
> + return 0;
> +}
> +
> +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 int virt_cpufreq_driver_remove(struct platform_device *pdev)
> +{
> + cpufreq_unregister_driver(&cpufreq_virt_driver);
> + return 0;
> +}
> +
> +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 {
> --
> 2.45.0.215.g3402c0e53f-goog
>
