base on sched_ext schedulers and tools # Sched_ext Schedulers and Tools [sched_ext](https://github.com/sched-ext/scx) is a Linux kernel feature which enables implementing kernel thread schedulers in BPF and dynamically loading them. This repository contains various scheduler implementations and support utilities. sched_ext enables safe and rapid iterations of scheduler implementations, thus radically widening the scope of scheduling strategies that can be experimented with and deployed; even in massive and complex production environments. You can find more information, links to blog posts and recordings, in the [wiki](https://github.com/sched-ext/scx/wiki). The following are a few highlights of this repository. - The [scx_layered case study](https://github.com/sched-ext/scx/blob/case-studies/case-studies/scx_layered.md) concretely demonstrates the power and benefits of sched_ext. - For a high-level but thorough overview of the sched_ext (especially its motivation), please refer to the [overview document](OVERVIEW.md). - For a description of the schedulers shipped with this tree, please refer to the [schedulers document](scheds/README.md). - The following video is the [scx_rustland](https://github.com/sched-ext/scx/tree/main/scheds/rust/scx_rustland) scheduler which makes most scheduling decisions in userspace Rust code showing better FPS in terraria while kernel is being compiled. This doesn't mean that scx_rustland is a better scheduler but does demonstrate how safe and easy it is to implement a scheduler which is generally usable and can outperform the default scheduler in certain scenarios. [scx_rustland-terraria](https://github.com/sched-ext/scx/assets/1051723/42ec3bf2-9f1f-4403-80ab-bf5d66b7c2d5) While the kernel feature is not upstream yet, we believe sched_ext has a reasonable chance of landing upstream in the foreseeable future. Both Meta and Google are fully committed to sched_ext and Meta is in the process of mass production deployment. See (#kernel-feature-status) for more details. In all example shell commands, `$SCX` refers to the root of this repository. ## Getting Started All that's necessary for running sched_ext schedulers is a kernel with sched_ext support and the scheduler binaries along with the libraries they depend on. Switching to a sched_ext scheduler is as simple as running a sched_ext binary: ``` root@test ~# cat /sys/kernel/sched_ext/state /sys/kernel/sched_ext/*/ops 2>/dev/null disabled root@test ~# scx_simple local=1 global=0 local=74 global=15 local=78 global=32 local=82 global=42 local=86 global=54 ^Zfish: Job 1, 'scx_simple' has stopped root@test ~# cat /sys/kernel/sched_ext/state /sys/kernel/sched_ext/*/ops 2>/dev/null enabled simple root@test ~# fg Send job 1 (scx_simple) to foreground local=635 global=179 local=696 global=192 ^CEXIT: BPF scheduler unregistered ``` [`scx_simple`](https://github.com/sched-ext/scx/blob/main/scheds/c/scx_simple.bpf.c) is a very simple global vtime scheduler which can behave acceptably on CPUs with a simple topology (single socket and single L3 cache domain). Above, we switch the whole system to use `scx_simple` by running the binary, suspend it with `ctrl-z` to confirm that it's loaded, and then switch back to the kernel default scheduler by terminating the process with `ctrl-c`. For `scx_simple`, suspending the scheduler process doesn't affect scheduling behavior because all that the userspace component does is print statistics. This doesn't hold for all schedulers. In addition to terminating the program, there are two more ways to disable a sched_ext scheduler - `sysrq-S` and the watchdog timer. Ignoring kernel bugs, the worst damage a sched_ext scheduler can do to a system is starving some threads until the watchdog timer triggers. As illustrated, once the kernel and binaries are in place, using sched_ext schedulers is straightforward and safe. While developing and building schedulers in this repository isn't complicated either, sched_ext makes use of many new BPF features, some of which require build tools which are newer than what many distros are currently shipping. This should become less of an issue in the future. For the time being, the following custom repositories are provided for select distros. ## Install Instructions by Distro - [Ubuntu](INSTALL.md#ubuntu) - [Arch Linux](INSTALL.md#arch-linux) - [Gentoo Linux](INSTALL.md#gentoo-linux) - [Fedora](INSTALL.md#fedora) - [Nix](INSTALL.md#nix) - [openSUSE Tumbleweed](INSTALL.md#opensuse-tumbleweed) ## Repository Structure ``` scx |-- scheds : Sched_ext scheduler implementations | |-- include : Shared BPF and user C include files including vmlinux.h | |-- c : Example schedulers - userspace code written C | \-- rust : Example schedulers - userspace code written Rust \-- rust : Rust support code \-- scx_utils : Common utility library for rust schedulers ``` ## Build & Install `meson` is the main build system but each Rust sub-project is its own self-contained cargo project and can be built and published separately. The followings are the dependencies and version requirements. **Note**: Many distros only have earlier versions of `meson`, in that case just [clone the meson repo](https://mesonbuild.com/Quick-guide.html#installation-from-source) and call `meson.py` e.g. `/path/to/meson/repo/meson.py compile -C build`. Alternatively, use `pip` e.g. `pip install meson` or `pip install meson --break-system-packages` (if needed). - `meson`: >=1.2, build scripts under `meson-scripts/` use `bash` and standard utilities including `awk`. - `clang`: >=16 required, >=17 recommended - `libbpf`: >=1.2.2 required, >=1.3 recommended (`RESIZE_ARRAY` support is new in 1.3). It's preferred to link statically against the source from the libbpf git repo, which is cloned during setup. - Rust toolchain: >=1.72 - `libelf`, `libz`, `libzstd` if linking against staic `libbpf.a` - `bpftool` By default this is cloned and built as part of the default build process. Alternatively it's usually available in `linux-tools-common`. The kernel has to be built with the following configuration: - `CONFIG_BPF=y` - `CONFIG_BPF_EVENTS=y` - `CONFIG_BPF_JIT=y` - `CONFIG_BPF_SYSCALL=y` - `CONFIG_DEBUG_INFO_BTF=y` - `CONFIG_FTRACE=y` - `CONFIG_SCHED_CLASS_EXT=y` ### Setting Up and Building `meson` always uses a separate build directory. Running the following commands in the root of the tree builds and installs all schedulers under `~/bin`. #### Static linking against libbpf (preferred) ``` $ cd $SCX $ meson setup build --prefix ~ $ meson compile -C build $ meson install -C build ``` Notes: `meson setup` will also clone both libbpf and bpftool repos and `meson compile` will build them both. Make sure you have dependencies installed that allow you to compile from source! ##### Ubuntu/Debian ``` apt install gcc-multilib build-essential libssl-dev llvm lld libelf-dev ``` ##### Arch Linux ``` pacman -S base-devel ``` ### Static linking against system libbpf Note, depending on your system configuration `libbpf_a` and `libbpf_h` may be in different directories. The system libbpf version needs to match the minimum libbpf version for scx. ``` $ cd $SCX $ meson setup build --prefix ~ -D libbpf_a=/usr/lib64/libbpf.a -D libbpf_h=/usr/include/bpf/ $ meson compile -C build $ meson install -C build ``` #### Dynamic linking against libbpf ``` $ cd $SCX $ meson setup build --prefix ~ -D libbpf_a=disabled $ meson compile -C build $ meson install -C build ``` #### Using a different bpftool This will check the system for an installed bpftool ``` $ meson setup build --prefix ~ -D bpftool=disabled ``` Using a custom built bpftool ``` $ meson setup build --prefix ~ -D bpftool=/path/to/bpftool ``` Note that `meson compile` step is not strictly necessary as `install` implies `compile`. The above also will build debug binaries with optimizations turned off, which is useful for development but they aren't optimized and big. For actual use you want to build release binaries. `meson` uses `-D` argument to specify build options. The configuration options can be specified at `setup` time but can also be changed afterwards and `meson` will do the right thing. To switch to release builds, run the following in the build directory and then compile and install again. ``` $ meson configure -Dbuildtype=release ``` Running `meson configure` without any argument shows all current build options. For more information on `meson` arguments and built-in options, please refer to `meson --help` and its [documentation](https://mesonbuild.com/Builtin-options.html). ### Building Specific Schedulers and Binary Locations If you just want to build a subset of schedulers, you can specify the scheduler names as arguments to `meson compile`. For example, if we just want to build the simple example scheduler `scheds/c/scx_simple` and the Rust userspace scheduler `scheds/rust/scx_rusty`: ``` $ cd $SCX $ meson setup build -Dbuildtype=release $ meson compile -C build scx_simple scx_rusty ``` :warning: **If your system has `sccache` installed**: `meson` automatically uses `sccache` if available. However, `sccache` fails in one of the build steps. If you encounter this issue, disable `sccache` by specifying `CC` directly - `$ CC=clang meson setup build -Dbuildtype=release`. You can also specify `-v` if you want to see the commands being used: ``` $ meson compile -C build -v scx_pair ``` For C userspace schedulers such as the ones under `scheds/c`, the built binaries are located in the same directory under the build root. For example, here, the `scx_simple` binary can be found at `$SCX/build/scheds/c/scx_simple`. For Rust userspace schedulers such as the ones under `scheds/rust`, the `scx_rusty` binary can be found at `$SCX/build/scheds/rust/release`. ### SCX specific build options While the default options should work in most cases, it may be desirable to override some of the toolchains and dependencies - e.g. to directly use `libbpf` built from the kernel source tree. The following `meson` build options can be used in such cases. - `bpf_clang`: `clang` to use when compiling `.bpf.c` - `bpftool`: `bpftool` to use when generating `.bpf.skel.h`. Set this to "disabled" to check the system for an already installed bpftool - `libbpf_a`: Static `libbpf.a` to use. Set this to "disabled" to link libbpf dynamically - `libbpf_h`: `libbpf` header directories, only meaningful with `libbpf_a` option - `cargo`: `cargo` to use when building rust sub-projects - 'cargo_home': 'CARGO_HOME env to use when invoking cargo' - `offline`: 'Compilation step should not access the internet' - `enable_rust`: 'Enable the build of rust sub-projects' For example, let's say you want to use `bpftool` and `libbpf` shipped in the kernel tree located at `$KERNEL`. We need to build `bpftool` in the kernel tree first, set up SCX build with the related options and then build & install. ``` $ cd $KERNEL $ make -C tools/bpf/bpftool $ cd $SCX $ BPFTOOL=$KERNEL/tools/bpf/bpftool $ meson setup build -Dbuildtype=release -Dprefix=~/bin \ -Dbpftool=$BPFTOOL/bpftool \ -Dlibbpf_a=$BPFTOOL/libbpf/libbpf.a \ -Dlibbpf_h=$BPFTOOL/libbpf/include $ meson install -C build ``` Note that we use `libbpf` which was produced as a part of `bpftool` build process rather than buliding `libbpf` directly. This is necessary because `libbpf` header files need to be installed for them to be in the expected relative locations. ### Offline Compilation Rust builds automatically download dependencies from crates.io; however, some build environments might not allow internet access requiring all dependencies to be available offline. The `fetch` target and `offline` option are provided for such cases. The following downloads all Rust dependencies into `$HOME/cargo-deps`. ``` $ cd $SCX $ meson setup build -Dcargo_home=$HOME/cargo-deps $ meson compile -C build fetch ``` The following builds the schedulers without accessing the internet. The `build` directory doesn't have to be the same one. The only requirement is that the `cargo_home` option points to a directory which contains the content generated from the previous step. ``` $ cd $SCX $ meson setup build -Dcargo_home=$HOME/cargo-deps -Doffline=true -Dbuildtype=release $ meson compile -C build ``` ### Working with Rust Sub-projects Each Rust sub-project is its own self-contained cargo project. When buildng as a part of this repository, `meson` invokes `cargo` with the appropriate options and environment variables to sync the build environment. When building separately by running `cargo build` directly in a sub-project directory, it will automatically figure out build environment. Please take a look at the [`scx_utils::BpfBuilder`](https://docs.rs/scx_utils/latest/scx_utils/struct.BpfBuilder.html) documentation for details. For example, the following builds and runs the `scx_rusty` scheduler: ``` $ cd $SCX/scheds/rust/scx_rusty $ cargo build --release $ cargo run --release ``` Here too, the `build` step is not strictly necessary as it's implied by `run`. Note that Rust userspace schedulers are published on `crates.io` and can be built and installed without cloning this repository as long as the necessary toolchains are available. Simply run: ``` $ cargo install --locked scx_rusty ``` and `scx_rusty` will be built and installed as `~/.cargo/bin/scx_rusty`. ## Checking scx_stats With the implementation of scx_stats, schedulers no longer display statistics by default. To display the statistics from the currently running scheduler, a manual user action is required. Below are examples of how to do this. - To check the scheduler statistics, use the ``` scx_SCHEDNAME --monitor $INTERVAL ``` for example 0.5 - this will print the output every half a second ``` scx_bpfland --monitor 0.5 ``` Some schedulers may implement different or multiple monitoring options. Refer to --help of each scheduler for details. Most schedulers also accept ` --stats $INTERVAL` to print the statistics directly from the scheduling instance. #### Examples - scx_bpfland ``` ❯ scx_bpfland --monitor 5 [scx_bpfland] tasks -> run: 3/4 int: 2 wait: 3 | nvcsw: 3 | dispatch -> dir: 0 prio: 73 shr: 9 [scx_bpfland] tasks -> run: 4/4 int: 2 wait: 2 | nvcsw: 3 | dispatch -> dir: 1 prio: 3498 shr: 1385 [scx_bpfland] tasks -> run: 4/4 int: 2 wait: 2 | nvcsw: 3 | dispatch -> dir: 1 prio: 2492 shr: 1311 [scx_bpfland] tasks -> run: 4/4 int: 2 wait: 3 | nvcsw: 3 | dispatch -> dir: 2 prio: 3270 shr: 1748 ``` - scx_rusty ``` ❯ scx_rusty --monitor 5 ###### Thu, 29 Aug 2024 14:42:37 +0200, load balance @ -265.1ms ###### cpu= 0.00 load= 0.17 mig=0 task_err=0 lb_data_err=0 time_used= 0.0ms tot= 15 sync_prev_idle= 0.00 wsync= 0.00 prev_idle= 0.00 greedy_idle= 0.00 pin= 0.00 dir= 0.00 dir_greedy= 0.00 dir_greedy_far= 0.00 dsq=100.00 greedy_local= 0.00 greedy_xnuma= 0.00 kick_greedy= 0.00 rep= 0.00 dl_clamp=33.33 dl_preset=93.33 slice=20000us direct_greedy_cpus=f kick_greedy_cpus=f NODE[00] load= 0.17 imbal= +0.00 delta= +0.00 DOM[00] load= 0.17 imbal= +0.00 delta= +0.00 ``` - scx_lavd ``` ❯ scx_lavd --monitor 5 | 12 | 1292 | 3 | 1 | 8510 | 37.6028 | 2.42068 | 99.1304 | 100 | 62.8907 | 100 | 100 | 62.8907 | performance | 100 | 0 | 0 | | 13 | 2208 | 3 | 1 | 6142 | 33.3442 | 2.39336 | 98.7626 | 100 | 60.2084 | 100 | 100 | 60.2084 | performance | 100 | 0 | 0 | | 14 | 941 | 3 | 1 | 5223 | 31.323 | 1.704 | 99.215 | 100.019 | 59.1614 | 100 | 100.019 | 59.1614 | performance | 100 | 0 | 0 | ``` - scx_rustland ``` ❯ scx_rustland --monitor 5 [RustLand] tasks -> r: 1/4 w: 3 /3 | pf: 0 | dispatch -> u: 4 k: 0 c: 0 b: 0 f: 0 | cg: 0 [RustLand] tasks -> r: 1/4 w: 2 /2 | pf: 0 | dispatch -> u: 28385 k: 0 c: 0 b: 0 f: 0 | cg: 0 [RustLand] tasks -> r: 0/4 w: 4 /0 | pf: 0 | dispatch -> u: 25288 k: 0 c: 0 b: 0 f: 0 | cg: 0 [RustLand] tasks -> r: 0/4 w: 2 /0 | pf: 0 | dispatch -> u: 30580 k: 0 c: 0 b: 0 f: 0 | cg: 0 [RustLand] tasks -> r: 0/4 w: 2 /0 | pf: 0 | dispatch -> u: 30824 k: 0 c: 0 b: 0 f: 0 | cg: 0 [RustLand] tasks -> r: 1/4 w: 1 /1 | pf: 0 | dispatch -> u: 33178 k: 0 c: 0 b: 0 f: 0 | cg: 0 ``` ## systemd services See: [services](services/README.md) ## Kernel Feature Status The kernel feature is not yet upstream and can be found in the [sched_ext](https://github.com/sched-ext/sched_ext) repository. The followings are important branches: - [`sched_ext`](https://github.com/sched-ext/sched_ext): The main development branch. This branch periodically pulls from the [bpf-next](https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/) tree to stay in sync with the kernel and BPF developments. - `sched_ext-release-*`: sched_ext backports on top of released kernels. We plan to maintain backports for a few recent kernel releases until sched_ext is merged upstream. Currently maintained backports: - [`sched_ext-release-v6.6`](https://github.com/sched-ext/sched_ext/tree/sched_ext-release-v6.6) - `sched_ext-vN`: Patchsets posted upstream. The v4 LKML thread has high-level discussions. - [RFC](https://github.com/htejun/sched_ext): [LMKL thread](http://lkml.kernel.org/r/[email protected]) - [`sched_ext-v2'](https://github.com/sched-ext/sched_ext/tree/sched_ext-v2): [LKML thread](http://lkml.kernel.org/r/[email protected]) - [`sched_ext-v3'](https://github.com/sched-ext/sched_ext/tree/sched_ext-v3): [LKML thread](http://lkml.kernel.org/r/[email protected]) - [`sched_ext-v4'](https://github.com/sched-ext/sched_ext/tree/sched_ext-v4): [LKML thread](http://lkml.kernel.org/r/[email protected]) - [`sched_ext-v5'](https://github.com/sched-ext/sched_ext/tree/sched_ext-v5): [LKML thread](http://lkml.kernel.org/r/[email protected]) ## [Breaking Changes](./BREAKING_CHANGES.md) [A list of the breaking changes](./BREAKING_CHANGES.md) in the sched_ext kernel tree and the associated commits for the schedulers in this repo. ## [Developer Guide](./DEVELOPER_GUIDE.md) Want to learn how to develop a scheduler or find some useful tools for working with schedulers? See the developer guide for more details. ## Getting in Touch We aim to build a friendly and approachable community around sched_ext. You can reach us through the following channels: - github: https://github.com/sched-ext/scx - Slack: [https://schedextworkspace.slack.com](https://join.slack.com/t/schedextworkspace/shared_invite/zt-24c4on3sk-sHlozdLfCZBODfwU6t6dbw) - Reddit: https://reddit.com/r/sched_ext We also hold weekly office hours every Tuesday. Please see the #office-hours channel on slack for details. To join the slack community, you can use [this link](https://bit.ly/scx_slack). ## Additional Resources There are blog posts and articles about sched_ext, which helps you to explore sched_ext in various ways. Followings are some examples: - [LWN: The extensible scheduler class (February, 2023)](https://lwn.net/Articles/922405/) - [arighi's blog: Implement your own kernel CPU scheduler in Ubuntu with sched-ext (July, 2023)](https://arighi.blogspot.com/2023/07/implement-your-own-cpu-scheduler-in.html) - [Changwoo's blog: sched_ext: a BPF-extensible scheduler class (Part 1) (December, 2023)](https://blogs.igalia.com/changwoo/sched-ext-a-bpf-extensible-scheduler-class-part-1/) - [arighi's blog: Getting started with sched-ext development (April, 2024)](https://arighi.blogspot.com/2024/04/getting-started-with-sched-ext.html) - [Changwoo's blog: sched_ext: scheduler architecture and interfaces (Part 2) (June, 2024)](https://blogs.igalia.com/changwoo/sched-ext-scheduler-architecture-and-interfaces-part-2/) - [arighi's YT channel: scx_bpfland Linux scheduler demo: topology awareness (August, 2024)](https://youtu.be/R-FEZOveG-I) ", Assign "at most 3 tags" to the expected json: {"id":"7020","tags":[]} "only from the tags list I provide: [{"id":77,"name":"3d"},{"id":89,"name":"agent"},{"id":17,"name":"ai"},{"id":54,"name":"algorithm"},{"id":24,"name":"api"},{"id":44,"name":"authentication"},{"id":3,"name":"aws"},{"id":27,"name":"backend"},{"id":60,"name":"benchmark"},{"id":72,"name":"best-practices"},{"id":39,"name":"bitcoin"},{"id":37,"name":"blockchain"},{"id":1,"name":"blog"},{"id":45,"name":"bundler"},{"id":58,"name":"cache"},{"id":21,"name":"chat"},{"id":49,"name":"cicd"},{"id":4,"name":"cli"},{"id":64,"name":"cloud-native"},{"id":48,"name":"cms"},{"id":61,"name":"compiler"},{"id":68,"name":"containerization"},{"id":92,"name":"crm"},{"id":34,"name":"data"},{"id":47,"name":"database"},{"id":8,"name":"declarative-gui "},{"id":9,"name":"deploy-tool"},{"id":53,"name":"desktop-app"},{"id":6,"name":"dev-exp-lib"},{"id":59,"name":"dev-tool"},{"id":13,"name":"ecommerce"},{"id":26,"name":"editor"},{"id":66,"name":"emulator"},{"id":62,"name":"filesystem"},{"id":80,"name":"finance"},{"id":15,"name":"firmware"},{"id":73,"name":"for-fun"},{"id":2,"name":"framework"},{"id":11,"name":"frontend"},{"id":22,"name":"game"},{"id":81,"name":"game-engine "},{"id":23,"name":"graphql"},{"id":84,"name":"gui"},{"id":91,"name":"http"},{"id":5,"name":"http-client"},{"id":51,"name":"iac"},{"id":30,"name":"ide"},{"id":78,"name":"iot"},{"id":40,"name":"json"},{"id":83,"name":"julian"},{"id":38,"name":"k8s"},{"id":31,"name":"language"},{"id":10,"name":"learning-resource"},{"id":33,"name":"lib"},{"id":41,"name":"linter"},{"id":28,"name":"lms"},{"id":16,"name":"logging"},{"id":76,"name":"low-code"},{"id":90,"name":"message-queue"},{"id":42,"name":"mobile-app"},{"id":18,"name":"monitoring"},{"id":36,"name":"networking"},{"id":7,"name":"node-version"},{"id":55,"name":"nosql"},{"id":57,"name":"observability"},{"id":46,"name":"orm"},{"id":52,"name":"os"},{"id":14,"name":"parser"},{"id":74,"name":"react"},{"id":82,"name":"real-time"},{"id":56,"name":"robot"},{"id":65,"name":"runtime"},{"id":32,"name":"sdk"},{"id":71,"name":"search"},{"id":63,"name":"secrets"},{"id":25,"name":"security"},{"id":85,"name":"server"},{"id":86,"name":"serverless"},{"id":70,"name":"storage"},{"id":75,"name":"system-design"},{"id":79,"name":"terminal"},{"id":29,"name":"testing"},{"id":12,"name":"ui"},{"id":50,"name":"ux"},{"id":88,"name":"video"},{"id":20,"name":"web-app"},{"id":35,"name":"web-server"},{"id":43,"name":"webassembly"},{"id":69,"name":"workflow"},{"id":87,"name":"yaml"}]" returns me the "expected json"