Merge 8997998571 into 65b49f8d30

fix compile errors

Cargo.lock

@@ -1700,6 +1700,23 @@ dependencies = [
  "simplelog",
 ]
 
+[[package]]
+name = "scx_flash"
+version = "1.0.4"
+dependencies = [
+ "anyhow",
+ "clap",
+ "crossbeam",
+ "ctrlc",
+ "libbpf-rs",
+ "log",
+ "scx_stats",
+ "scx_stats_derive",
+ "scx_utils",
+ "serde",
+ "simplelog",
+]
+
 [[package]]
 name = "scx_lavd"
 version = "1.0.6"

Cargo.toml

@@ -6,6 +6,7 @@ members = ["rust/scx_stats",
            "rust/scx_loader",
 	   "scheds/rust/scx_lavd",
            "scheds/rust/scx_bpfland",
+           "scheds/rust/scx_flash",
            "scheds/rust/scx_rustland",
            "scheds/rust/scx_rlfifo",
            "scheds/rust/scx_rusty",

OVERVIEW.md

@@ -77,9 +77,9 @@ enabling custom, userspace driven scheduling policies. Prior
 [presentations](https://lpc.events/event/16/contributions/1365/) at LPC have
 discussed ghOSt and how BPF can be used to accelerate scheduling.
 
-### Why can't we just explore directly with CFS?
+### Why can't we just explore directly with EEVDF?
 
-Experimenting with CFS directly or implementing a new sched_class from scratch
+Experimenting with EEVDF directly or implementing a new sched_class from scratch
 is of course possible, but is often difficult and time consuming. Newcomers to
 the scheduler often require years to understand the codebase and become
 productive contributors. Even for seasoned kernel engineers, experimenting with
@@ -200,17 +200,17 @@ throughput improvement on an Nginx benchmark, with an 87% inference accuracy.
 This section discusses how sched_ext can enable users to run workloads on
 application-specific schedulers.
 
-### Why deploy custom schedulers rather than improving CFS?
+### Why deploy custom schedulers rather than improving EEVDF?
 
-Implementing application-specific schedulers and improving CFS are not
+Implementing application-specific schedulers and improving EEVDF are not
 conflicting goals. Scheduling features explored with sched_ext which yield
 beneficial results, and which are sufficiently generalizable, can and should
-be integrated into CFS. However, CFS is fundamentally designed to be a general
+be integrated into EEVDF. However, EEVDF is fundamentally designed to be a general
 purpose scheduler, and thus is not conducive to being extended with some
 highly targeted application or hardware specific changes.
 
 Targeted, bespoke scheduling has many potential use cases. For example, VM
-scheduling can make certain optimizations that are infeasible in CFS due to
+scheduling can make certain optimizations that are infeasible in EEVDF due to
 the constrained problem space (scheduling a static number of long-running
 VCPUs versus an arbitrary number of threads). Additionally, certain
 applications might want to make targeted policy decisions based on hints
@@ -236,9 +236,9 @@ bounded tail latencies, as well as longer blocks of uninterrupted time.
 Yet another interesting use case is the scx_flatcg scheduler, which provides a
 flattened hierarchical vtree for cgroups. This scheduler does not account for
 thundering herd problems among cgroups, and therefore may not be suitable for
-inclusion in CFS. However, in a simple benchmark using
+inclusion in EEVDF. However, in a simple benchmark using
 [wrk](https://github.com/wg/wrk) on apache serving a CGI script calculating
-sha1sum of a small file, it outperformed CFS by ~3% with CPU controller
+sha1sum of a small file, it outperformed EEVDF by ~3% with CPU controller
 disabled and by ~10% with two apache instances competing with 2:1 weight ratio
 nested four level deep.
 
@@ -327,7 +327,7 @@ affinity to limit the footprint of this low-priority workload to a small subset
 of CPUs, a preferable solution would be to implement a more featureful
 task-priority mechanism which automatically throttles lower-priority tasks
 which are causing memory contention for the rest of the system. Implementing
-this in CFS and rolling it out to the fleet could take a very long time.
+this in EEVDF and rolling it out to the fleet could take a very long time.
 
 sched_ext would directly address these gaps. If another hardware bug or
 resource contention issue comes in that requires scheduler support to mitigate,

README.md

@@ -176,7 +176,7 @@ 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 libbpf_h=/usr/include/bpf/
+$ 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
 ```

meson-scripts/stress_tests.ini

@@ -22,6 +22,12 @@ sched_args: -v
 stress_cmd: stress-ng -t 14 --aggressive -M -c `nproc` -f `nproc`
 timeout_sec: 15
 
+[scx_flash]
+sched: scx_flash
+sched_args:
+stress_cmd: stress-ng -t 14 --aggressive -M -c `nproc` -f `nproc`
+timeout_sec: 15
+
 [scx_layered]
 sched: scx_layered
 sched_args: --run-example -v --stats 1

meson.build

@@ -327,7 +327,7 @@ if enable_rust
   run_target('fetch', command: [cargo_fetch, cargo], env: cargo_env)
 
   rust_scheds = ['scx_lavd', 'scx_bpfland', 'scx_rustland', 'scx_rlfifo',
-                 'scx_rusty',
+                 'scx_flash', 'scx_rusty',
                  'scx_layered', 'scx_mitosis']
   rust_misc = ['scx_stats', 'scx_stats_derive', 'scx_utils',
                'scx_rustland_core',

scheds/rust/README.md

@@ -18,3 +18,4 @@ main.rs or \*.bpf.c files.
 - [scx_rlfifo](scx_rlfifo/README.md)
 - [scx_lavd](scx_lavd/README.md)
 - [scx_bpfland](scx_bpfland/README.md)
+- [scx_flash](scx_flash/README.md)

scheds/rust/scx_flash/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "scx_flash"
+version = "1.0.4"
+authors = ["Andrea Righi <arighi@nvidia.com>"]
+edition = "2021"
+description = "A scheduler designed for multimedia and real-time audio processing workloads. https://github.com/sched-ext/scx/tree/main"
+license = "GPL-2.0-only"
+
+[dependencies]
+anyhow = "1.0.65"
+ctrlc = { version = "3.1", features = ["termination"] }
+clap = { version = "4.1", features = ["derive", "env", "unicode", "wrap_help"] }
+crossbeam = "0.8.4"
+libbpf-rs = "0.24.1"
+log = "0.4.17"
+scx_stats = { path = "../../../rust/scx_stats", version = "1.0.4" }
+scx_stats_derive = { path = "../../../rust/scx_stats/scx_stats_derive", version = "1.0.4" }
+scx_utils = { path = "../../../rust/scx_utils", version = "1.0.4" }
+serde = { version = "1.0", features = ["derive"] }
+simplelog = "0.12"
+
+[build-dependencies]
+scx_utils = { path = "../../../rust/scx_utils", version = "1.0.4" }
+
+[features]
+enable_backtrace = []

scheds/rust/scx_flash/LICENSE

@@ -0,0 +1 @@
+../../../LICENSE

scheds/rust/scx_flash/README.md

@@ -0,0 +1,26 @@
+# scx_flash
+
+This is a single user-defined scheduler used within [sched_ext](https://github.com/sched-ext/scx/tree/main), which is a Linux kernel feature which enables implementing kernel thread schedulers in BPF and dynamically loading them. [Read more about sched_ext](https://github.com/sched-ext/scx/tree/main).
+
+## Overview
+
+A scheduler that focuses on ensuring fairness among tasks and performance
+predictability.
+
+It operates using an earliest deadline first (EDF) policy, where each task is
+assigned a "latency" weight. This weight is dynamically adjusted based on how
+often a task release the CPU before its full time slice is used. Tasks that
+release the CPU early are given a higher latency weight, prioritizing them over
+tasks that fully consume their time slice.
+
+## Typical Use Case
+
+The combination of dynamic latency weights and EDF scheduling ensures
+responsive and consistent performance, even in overcommitted systems.
+
+This makes the scheduler particularly well-suited for latency-sensitive
+workloads, such as multimedia or real-time audio processing.
+
+## Production Ready?
+
+Yes.

scheds/rust/scx_flash/build.rs

@@ -0,0 +1,13 @@
+// Copyright (c) Andrea Righi <arighi@nvidia.com>
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2.
+
+fn main() {
+    scx_utils::BpfBuilder::new()
+        .unwrap()
+        .enable_intf("src/bpf/intf.h", "bpf_intf.rs")
+        .enable_skel("src/bpf/main.bpf.c", "bpf")
+        .build()
+        .unwrap();
+}

scheds/rust/scx_flash/rustfmt.toml

@@ -0,0 +1,8 @@
+# Get help on options with `rustfmt --help=config`
+# Please keep these in alphabetical order.
+edition = "2021"
+group_imports = "StdExternalCrate"
+imports_granularity = "Item"
+merge_derives = false
+use_field_init_shorthand = true
+version = "Two"

scheds/rust/scx_flash/src/bpf/intf.h

@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
+ *
+ * This software may be used and distributed according to the terms of the GNU
+ * General Public License version 2.
+ */
+#ifndef __INTF_H
+#define __INTF_H
+
+#include <limits.h>
+
+#define MAX(x, y) ((x) > (y) ? (x) : (y))
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+#define CLAMP(val, lo, hi) MIN(MAX(val, lo), hi)
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+enum consts {
+	NSEC_PER_USEC = 1000ULL,
+	NSEC_PER_MSEC = (1000ULL * NSEC_PER_USEC),
+	NSEC_PER_SEC = (1000ULL * NSEC_PER_MSEC),
+};
+
+#ifndef __VMLINUX_H__
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned int u32;
+typedef unsigned long u64;
+
+typedef signed char s8;
+typedef signed short s16;
+typedef signed int s32;
+typedef signed long s64;
+
+typedef int pid_t;
+#endif /* __VMLINUX_H__ */
+
+struct domain_arg {
+	s32 cpu_id;
+	s32 sibling_cpu_id;
+};
+
+#endif /* __INTF_H */

scheds/rust/scx_flash/src/bpf_intf.rs

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
+
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2.
+#![allow(non_upper_case_globals)]
+#![allow(non_camel_case_types)]
+#![allow(non_snake_case)]
+#![allow(dead_code)]
+
+include!(concat!(env!("OUT_DIR"), "/bpf_intf.rs"));

scheds/rust/scx_flash/src/bpf_skel.rs

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
+
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2.
+
+include!(concat!(env!("OUT_DIR"), "/bpf_skel.rs"));

scheds/rust/scx_flash/src/main.rs

@@ -0,0 +1,334 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
+
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2.
+
+mod bpf_skel;
+pub use bpf_skel::*;
+pub mod bpf_intf;
+pub use bpf_intf::*;
+
+mod stats;
+use std::collections::HashMap;
+use std::ffi::c_int;
+use std::fs::File;
+use std::io::Read;
+use std::mem::MaybeUninit;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
+use std::time::Duration;
+
+use anyhow::bail;
+use anyhow::Context;
+use anyhow::Result;
+use clap::Parser;
+use crossbeam::channel::RecvTimeoutError;
+use libbpf_rs::skel::OpenSkel;
+use libbpf_rs::skel::Skel;
+use libbpf_rs::skel::SkelBuilder;
+use libbpf_rs::OpenObject;
+use libbpf_rs::ProgramInput;
+use log::info;
+use log::warn;
+use scx_stats::prelude::*;
+use scx_utils::build_id;
+use scx_utils::import_enums;
+use scx_utils::scx_enums;
+use scx_utils::scx_ops_attach;
+use scx_utils::scx_ops_load;
+use scx_utils::scx_ops_open;
+use scx_utils::set_rlimit_infinity;
+use scx_utils::uei_exited;
+use scx_utils::uei_report;
+use scx_utils::Topology;
+use scx_utils::UserExitInfo;
+use stats::Metrics;
+
+const SCHEDULER_NAME: &'static str = "scx_flash";
+
+#[derive(Debug, Parser)]
+struct Opts {
+    /// Exit debug dump buffer length. 0 indicates default.
+    #[clap(long, default_value = "0")]
+    exit_dump_len: u32,
+
+    /// Maximum scheduling slice duration in microseconds.
+    #[clap(short = 's', long, default_value = "20000")]
+    slice_us_max: u64,
+
+    /// Maximum time slice lag in microseconds.
+    ///
+    /// Increasing this value can help to enhance the responsiveness of interactive tasks, but it
+    /// can also make performance more "spikey".
+    #[clap(short = 'l', long, default_value = "20000")]
+    slice_us_lag: u64,
+
+    /// Enable kthreads prioritization.
+    ///
+    /// Enabling this can improve system performance, but it may also introduce interactivity
+    /// issues or unfairness in scenarios with high kthread activity, such as heavy I/O or network
+    /// traffic.
+    #[clap(short = 'k', long, action = clap::ArgAction::SetTrue)]
+    local_kthreads: bool,
+
+    /// Enable stats monitoring with the specified interval.
+    #[clap(long)]
+    stats: Option<f64>,
+
+    /// Run in stats monitoring mode with the specified interval. Scheduler
+    /// is not launched.
+    #[clap(long)]
+    monitor: Option<f64>,
+
+    /// Enable verbose output, including libbpf details.
+    #[clap(short = 'v', long, action = clap::ArgAction::SetTrue)]
+    verbose: bool,
+
+    /// Print scheduler version and exit.
+    #[clap(short = 'V', long, action = clap::ArgAction::SetTrue)]
+    version: bool,
+
+    /// Show descriptions for statistics.
+    #[clap(long)]
+    help_stats: bool,
+}
+
+fn is_smt_active() -> std::io::Result<i32> {
+    let mut file = File::open("/sys/devices/system/cpu/smt/active")?;
+    let mut contents = String::new();
+    file.read_to_string(&mut contents)?;
+
+    let smt_active: i32 = contents.trim().parse().unwrap_or(0);
+
+    Ok(smt_active)
+}
+
+struct Scheduler<'a> {
+    skel: BpfSkel<'a>,
+    struct_ops: Option<libbpf_rs::Link>,
+    stats_server: StatsServer<(), Metrics>,
+}
+
+impl<'a> Scheduler<'a> {
+    fn init(opts: &'a Opts, open_object: &'a mut MaybeUninit<OpenObject>) -> Result<Self> {
+        set_rlimit_infinity();
+
+        // Check host topology to determine if we need to enable SMT capabilities.
+        let smt_enabled = match is_smt_active() {
+            Ok(value) => value == 1,
+            Err(e) => bail!("Failed to read SMT status: {}", e),
+        };
+        info!(
+            "{} {} {}",
+            SCHEDULER_NAME,
+            *build_id::SCX_FULL_VERSION,
+            if smt_enabled { "SMT on" } else { "SMT off" }
+        );
+
+        // Initialize BPF connector.
+        let mut skel_builder = BpfSkelBuilder::default();
+        skel_builder.obj_builder.debug(opts.verbose);
+        let mut skel = scx_ops_open!(skel_builder, open_object, flash_ops)?;
+
+        skel.struct_ops.flash_ops_mut().exit_dump_len = opts.exit_dump_len;
+
+        // Override default BPF scheduling parameters.
+        skel.maps.rodata_data.slice_max = opts.slice_us_max * 1000;
+        skel.maps.rodata_data.slice_lag = opts.slice_us_lag * 1000;
+        skel.maps.rodata_data.local_kthreads = opts.local_kthreads;
+
+        skel.maps.rodata_data.smt_enabled = smt_enabled;
+
+        // Load the BPF program for validation.
+        let mut skel = scx_ops_load!(skel, flash_ops, uei)?;
+
+        // Initialize CPU topology.
+        let topo = Topology::new().unwrap();
+
+        // Initialize LLC domain.
+        Self::init_l3_cache_domains(&mut skel, &topo)?;
+
+        // Attach the scheduler.
+        let struct_ops = Some(scx_ops_attach!(skel, flash_ops)?);
+        let stats_server = StatsServer::new(stats::server_data()).launch()?;
+
+        Ok(Self {
+            skel,
+            struct_ops,
+            stats_server,
+        })
+    }
+
+    fn enable_sibling_cpu(
+        skel: &mut BpfSkel<'_>,
+        cpu: usize,
+        sibling_cpu: usize,
+    ) -> Result<(), u32> {
+        let prog = &mut skel.progs.enable_sibling_cpu;
+        let mut args = domain_arg {
+            cpu_id: cpu as c_int,
+            sibling_cpu_id: sibling_cpu as c_int,
+        };
+        let input = ProgramInput {
+            context_in: Some(unsafe {
+                std::slice::from_raw_parts_mut(
+                    &mut args as *mut _ as *mut u8,
+                    std::mem::size_of_val(&args),
+                )
+            }),
+            ..Default::default()
+        };
+        let out = prog.test_run(input).unwrap();
+        if out.return_value != 0 {
+            return Err(out.return_value);
+        }
+
+        Ok(())
+    }
+
+    fn init_cache_domains(
+        skel: &mut BpfSkel<'_>,
+        topo: &Topology,
+        cache_lvl: usize,
+        enable_sibling_cpu_fn: &dyn Fn(&mut BpfSkel<'_>, usize, usize, usize) -> Result<(), u32>,
+    ) -> Result<(), std::io::Error> {
+        // Determine the list of CPU IDs associated to each cache node.
+        let mut cache_id_map: HashMap<usize, Vec<usize>> = HashMap::new();
+        for core in topo.cores().into_iter() {
+            for (cpu_id, cpu) in core.cpus() {
+                let cache_id = match cache_lvl {
+                    2 => cpu.l2_id(),
+                    3 => cpu.l3_id(),
+                    _ => panic!("invalid cache level {}", cache_lvl),
+                };
+                cache_id_map
+                    .entry(cache_id)
+                    .or_insert_with(Vec::new)
+                    .push(*cpu_id);
+            }
+        }
+
+        // Update the BPF cpumasks for the cache domains.
+        for (cache_id, cpus) in cache_id_map {
+            info!(
+                "L{} cache ID {}: sibling CPUs: {:?}",
+                cache_lvl, cache_id, cpus
+            );
+            for cpu in &cpus {
+                for sibling_cpu in &cpus {
+                    match enable_sibling_cpu_fn(skel, cache_lvl, *cpu, *sibling_cpu) {
+                        Ok(()) => {}
+                        Err(_) => {
+                            warn!(
+                                "L{} cache ID {}: failed to set CPU {} sibling {}",
+                                cache_lvl, cache_id, *cpu, *sibling_cpu
+                            );
+                        }
+                    }
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn init_l3_cache_domains(
+        skel: &mut BpfSkel<'_>,
+        topo: &Topology,
+    ) -> Result<(), std::io::Error> {
+        Self::init_cache_domains(skel, topo, 3, &|skel, _lvl, cpu, sibling_cpu| {
+            Self::enable_sibling_cpu(skel, cpu, sibling_cpu)
+        })
+    }
+
+    fn get_metrics(&self) -> Metrics {
+        Metrics {
+            nr_kthread_dispatches: self.skel.maps.bss_data.nr_kthread_dispatches,
+            nr_direct_dispatches: self.skel.maps.bss_data.nr_direct_dispatches,
+            nr_shared_dispatches: self.skel.maps.bss_data.nr_shared_dispatches,
+        }
+    }
+
+    pub fn exited(&mut self) -> bool {
+        uei_exited!(&self.skel, uei)
+    }
+
+    fn run(&mut self, shutdown: Arc<AtomicBool>) -> Result<UserExitInfo> {
+        let (res_ch, req_ch) = self.stats_server.channels();
+        while !shutdown.load(Ordering::Relaxed) && !self.exited() {
+            match req_ch.recv_timeout(Duration::from_secs(1)) {
+                Ok(()) => res_ch.send(self.get_metrics())?,
+                Err(RecvTimeoutError::Timeout) => {}
+                Err(e) => Err(e)?,
+            }
+        }
+
+        self.struct_ops.take();
+        uei_report!(&self.skel, uei)
+    }
+}
+
+impl<'a> Drop for Scheduler<'a> {
+    fn drop(&mut self) {
+        info!("Unregister {} scheduler", SCHEDULER_NAME);
+    }
+}
+
+fn main() -> Result<()> {
+    let opts = Opts::parse();
+
+    if opts.version {
+        println!("{} {}", SCHEDULER_NAME, *build_id::SCX_FULL_VERSION);
+        return Ok(());
+    }
+
+    if opts.help_stats {
+        stats::server_data().describe_meta(&mut std::io::stdout(), None)?;
+        return Ok(());
+    }
+
+    let loglevel = simplelog::LevelFilter::Info;
+
+    let mut lcfg = simplelog::ConfigBuilder::new();
+    lcfg.set_time_level(simplelog::LevelFilter::Error)
+        .set_location_level(simplelog::LevelFilter::Off)
+        .set_target_level(simplelog::LevelFilter::Off)
+        .set_thread_level(simplelog::LevelFilter::Off);
+    simplelog::TermLogger::init(
+        loglevel,
+        lcfg.build(),
+        simplelog::TerminalMode::Stderr,
+        simplelog::ColorChoice::Auto,
+    )?;
+
+    let shutdown = Arc::new(AtomicBool::new(false));
+    let shutdown_clone = shutdown.clone();
+    ctrlc::set_handler(move || {
+        shutdown_clone.store(true, Ordering::Relaxed);
+    })
+    .context("Error setting Ctrl-C handler")?;
+
+    if let Some(intv) = opts.monitor.or(opts.stats) {
+        let shutdown_copy = shutdown.clone();
+        let jh = std::thread::spawn(move || {
+            stats::monitor(Duration::from_secs_f64(intv), shutdown_copy).unwrap()
+        });
+        if opts.monitor.is_some() {
+            let _ = jh.join();
+            return Ok(());
+        }
+    }
+
+    let mut open_object = MaybeUninit::uninit();
+    loop {
+        let mut sched = Scheduler::init(&opts, &mut open_object)?;
+        if !sched.run(shutdown.clone())?.should_restart() {
+            break;
+        }
+    }
+
+    Ok(())
+}

scheds/rust/scx_flash/src/stats.rs

@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (c) 2024 Andrea Righi <arighi@nvidia.com>
+
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2.
+
+use std::io::Write;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
+use std::time::Duration;
+
+use anyhow::Result;
+use scx_stats::prelude::*;
+use scx_stats_derive::Stats;
+use serde::Deserialize;
+use serde::Serialize;
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize, Stats)]
+#[stat(top)]
+pub struct Metrics {
+    #[stat(desc = "Number of kthread direct dispatches")]
+    pub nr_kthread_dispatches: u64,
+    #[stat(desc = "Number of task direct dispatches")]
+    pub nr_direct_dispatches: u64,
+    #[stat(desc = "Number of task global dispatches")]
+    pub nr_shared_dispatches: u64,
+}
+
+impl Metrics {
+    fn format<W: Write>(&self, w: &mut W) -> Result<()> {
+        writeln!(
+            w,
+            "[{}] dispatch -> kthread: {:<5} direct: {:<5} shared: {:<5}",
+            crate::SCHEDULER_NAME,
+            self.nr_kthread_dispatches,
+            self.nr_direct_dispatches,
+            self.nr_shared_dispatches,
+        )?;
+        Ok(())
+    }
+
+    fn delta(&self, rhs: &Self) -> Self {
+        Self {
+            nr_kthread_dispatches: self.nr_kthread_dispatches - rhs.nr_kthread_dispatches,
+            nr_direct_dispatches: self.nr_direct_dispatches - rhs.nr_direct_dispatches,
+            nr_shared_dispatches: self.nr_shared_dispatches - rhs.nr_shared_dispatches,
+            ..self.clone()
+        }
+    }
+}
+
+pub fn server_data() -> StatsServerData<(), Metrics> {
+    let open: Box<dyn StatsOpener<(), Metrics>> = Box::new(move |(req_ch, res_ch)| {
+        req_ch.send(())?;
+        let mut prev = res_ch.recv()?;
+
+        let read: Box<dyn StatsReader<(), Metrics>> = Box::new(move |_args, (req_ch, res_ch)| {
+            req_ch.send(())?;
+            let cur = res_ch.recv()?;
+            let delta = cur.delta(&prev);
+            prev = cur;
+            delta.to_json()
+        });
+
+        Ok(read)
+    });
+
+    StatsServerData::new()
+        .add_meta(Metrics::meta())
+        .add_ops("top", StatsOps { open, close: None })
+}
+
+pub fn monitor(intv: Duration, shutdown: Arc<AtomicBool>) -> Result<()> {
+    scx_utils::monitor_stats::<Metrics>(
+        &vec![],
+        intv,
+        || shutdown.load(Ordering::Relaxed),
+        |metrics| metrics.format(&mut std::io::stdout()),
+    )
+}

services/scx

@@ -1,4 +1,4 @@
-# List of scx_schedulers: scx_bpfland scx_central scx_lavd scx_layered scx_nest scx_qmap scx_rlfifo scx_rustland scx_rusty scx_simple scx_userland
+# List of scx_schedulers: scx_bpfland scx_central scx_flash scx_lavd scx_layered scx_nest scx_qmap scx_rlfifo scx_rustland scx_rusty scx_simple scx_userland
 SCX_SCHEDULER=scx_bpfland
 
 # Set custom flags for each scheduler, below is an example of how to use