(cc'ing Daniel Hodges and quoting the whole body) On Sun, Sep 29, 2024 at 09:56:02AM -0700, Alexei Starovoitov wrote: > On Fri, Sep 27, 2024 at 3:03 AM Yipeng Zou <zouyipeng@xxxxxxxxxx> wrote: > > > > Hi everyone, > > > > I am currently working on a patch for a CPU frequency governor based on > > BPF, which can use BPF to customize and implement various frequency > > scaling strategies. > > > > If you have any feedback or suggestions, please do let me know. > > > > Motivation > > ---------- > > > > 1. Customization > > > > Existing cpufreq governors in the kernel are designed for general > > scenarios, which may not always be optimal for specific or specialized > > workloads. > > > > The userspace governor allows direct control over cpufreq, but users > > often require guidance from the kernel to achieve the desired frequency. > > > > Cpufreq_ext aims to address this by providing a customizable framework that > > can be tailored to the unique needs of different systems and applications. > > > > While cpufreq governors can be implemented within a kernel module, > > maintaining a ko tailored for specific scenarios can be challenging. > > The complexity and overhead associated with kernel modules make it > > difficult to quickly adapt and deploy custom frequency scaling strategies. > > > > Cpufreq_ext leverages BPF to offer a more lightweight and flexible approach > > to implementing customized strategies, allowing for easier maintenance and > > deployment. > > > > 2. Integration with sched_ext: > > > > sched_ext is a scheduler class whose behavior can be defined by a set of > > BPF programs - the BPF scheduler. > > > > Look for more about sched_ext in [1]: > > > > [1] https://www.kernel.org/doc/html/next/scheduler/sched-ext.html > > > > The interaction between CPU frequency scaling and task scheduling is > > critical for performance. > > > > cpufreq_ext can work with sched_ext to ensure that both scheduling > > decisions and frequency adjustments are made in a coordinated manner, > > optimizing system responsiveness and power consumption. > > I think sched-ext already has a mechanism to influence cpufreq. > How is this different ? FWIW, sched_ext's cpufreq implementation is through the schedutil governor. All that the BPF scheduler does is providing utilization signal to the governor. This seems to work fine for sched_ext schedulers (this doesn't preclude more direct BPF governor). > Pls cc sched-ext folks in the future. Yeah, it'd be great if you can cc Daniel, me and sched-ext@xxxxxxxx. > > Overview > > -------- > > > > The cpufreq ext is a BPF based cpufreq governor, we can customize > > cpufreq governor in BPF program. > > > > CPUFreq ext works as common cpufreq governor with cpufreq policy. > > > > -------------------------- > > | BPF governor | > > -------------------------- > > | > > v > > BPF Register > > | > > v > > -------------------------------------- > > | CPUFreq ext | > > -------------------------------------- > > ^ ^ ^ > > | | | > > --------- --------- --------- > > | policy0 | ... | policy1 | ... | policyn | > > --------- --------- --------- > > > > We can register serval function hooks to cpufreq ext by BPF Struct OPS. > > > > The first patch define a dbs_governor, and it's works like other > > governor. > > > > The second patch gives a sample how to use it, implement one > > typical cpufreq governor, switch to max cpufreq when VIP task > > is running on target cpu. > > > > Detail > > ------ > > > > The cpufreq ext use bpf_struct_ops to register serval function hooks. > > > > struct cpufreq_governor_ext_ops { > > ... > > } > > > > Cpufreq_governor_ext_ops defines all the functions that BPF programs can > > implement customly. > > > > If you need to add a custom function, you only need to define it in this > > struct. > > > > At the moment we have defined the basic functions. > > > > 1. unsigned long (*get_next_freq)(struct cpufreq_policy *policy) > > > > Make decision how to adjust cpufreq here. > > The return value represents the CPU frequency that will be > > updated. > > > > 2. unsigned int (*get_sampling_rate)(struct cpufreq_policy *policy) > > > > Make decision how to adjust sampling_rate here. > > The return value represents the governor samplint rate that > > will be updated. > > > > 3. unsigned int (*init)(void) > > > > BPF governor init callback, return 0 means success. > > > > 4. void (*exit)(void) > > > > BPF governor exit callback. > > > > 5. char name[CPUFREQ_EXT_NAME_LEN] > > > > BPF governor name. > > > > The cpufreq_ext also add sysfs interface which refer to governor status. > > > > 1. ext/stat attribute: > > > > Access to current BPF governor status. > > > > # cat /sys/devices/system/cpu/cpufreq/ext/stat > > Stat: CPUFREQ_EXT_INIT > > BPF governor: performance > > > > There are number of constraints on the cpufreq_ext: > > > > 1. Only one ext governor can be registered at a time. > > > > 2. By default, it operates as a performance governor when no BPF > > governor is registered. > > > > 3. The cpufreq_ext governor must be selected before loading a BPF > > governor; otherwise, the installation of the BPF governor will fail. > > > > TODO > > ---- > > > > The current patch is a starting point, and future work will focus on > > expanding its capabilities. > > > > I plan to leverage the BPF ecosystem to introduce innovative features, > > such as real-time adjustments and optimizations based on system-wide > > observations and analytics. > > > > And I am looking forward to any insights, critiques, or suggestions you > > may have. > > > > Yipeng Zou (2): > > cpufreq_ext: Introduce cpufreq ext governor > > cpufreq_ext: Add bpf sample > > > > drivers/cpufreq/Kconfig | 23 ++ > > drivers/cpufreq/Makefile | 1 + > > drivers/cpufreq/cpufreq_ext.c | 525 +++++++++++++++++++++++++++++++++ > > samples/bpf/.gitignore | 1 + > > samples/bpf/Makefile | 8 +- > > samples/bpf/cpufreq_ext.bpf.c | 113 +++++++ > > samples/bpf/cpufreq_ext_user.c | 48 +++ > > 7 files changed, 718 insertions(+), 1 deletion(-) > > create mode 100644 drivers/cpufreq/cpufreq_ext.c > > create mode 100644 samples/bpf/cpufreq_ext.bpf.c > > create mode 100644 samples/bpf/cpufreq_ext_user.c > > > > -- > > 2.34.1 > > -- tejun
