From 0cb1ffe0258380a3dd25c1037fdfb6ceca3149d9 Mon Sep 17 00:00:00 2001 From: James Munns Date: Wed, 16 Apr 2025 17:58:45 +0200 Subject: Add EDF example --- examples/nrf52840-edf/src/bin/basic.rs | 191 +++++++++++++++++++++++++++++++++ 1 file changed, 191 insertions(+) create mode 100644 examples/nrf52840-edf/src/bin/basic.rs (limited to 'examples/nrf52840-edf/src/bin/basic.rs') diff --git a/examples/nrf52840-edf/src/bin/basic.rs b/examples/nrf52840-edf/src/bin/basic.rs new file mode 100644 index 000000000..6a7eb3c4b --- /dev/null +++ b/examples/nrf52840-edf/src/bin/basic.rs @@ -0,0 +1,191 @@ +//! Basic side-by-side example of the Earliest Deadline First scheduler +//! +//! This test spawns a number of background "ambient system load" workers +//! that are constantly working, and runs two sets of trials. +//! +//! The first trial runs with no deadline set, so our trial task is at the +//! same prioritization level as the background worker tasks. +//! +//! The second trial sets a deadline, meaning that it will be given higher +//! scheduling priority than background tasks, that have no deadline set + +#![no_std] +#![no_main] + +use core::sync::atomic::{compiler_fence, Ordering}; +use embassy_executor::{raw::Deadline, Spawner}; +use embassy_time::{Duration, Instant, Timer}; +use {defmt_rtt as _, panic_probe as _}; + +#[embassy_executor::main] +async fn main(spawner: Spawner) { + embassy_nrf::init(Default::default()); + + // Enable flash cache to remove some flash latency jitter + compiler_fence(Ordering::SeqCst); + embassy_nrf::pac::NVMC.icachecnf().write(|w| { + w.set_cacheen(true); + }); + compiler_fence(Ordering::SeqCst); + + // + // Baseline system load tunables + // + + // how many load tasks? More load tasks means more tasks contending + // for the runqueue + let tasks = 32; + // how long should each task work for? The longer the working time, + // the longer the max jitter possible, even when a task is prioritized, + // as EDF is still cooperative and not pre-emptive + // + // 33 ticks ~= 1ms + let work_time_ticks = 33; + // what fraction, 1/denominator, should the system be busy? + // bigger number means **less** busy + // + // 2 => 50% + // 4 => 25% + // 10 => 10% + let denominator = 2; + + // Total time window, so each worker is working 1/denominator + // amount of the total time + let time_window = work_time_ticks * u64::from(tasks) * denominator; + + // Spawn all of our load workers! + for i in 0..tasks { + spawner.must_spawn(load_task(i, work_time_ticks, time_window)); + } + + // Let all the tasks spin up + defmt::println!("Spinning up load tasks..."); + Timer::after_secs(1).await; + + // + // Trial task worker tunables + // + + // How many steps should the workers under test run? + // More steps means more chances to have to wait for other tasks + // in line ahead of us. + let num_steps = 100; + + // How many ticks should the worker take working on each step? + // + // 33 ticks ~= 1ms + let work_ticks = 33; + // How many ticks should the worker wait on each step? + // + // 66 ticks ~= 2ms + let idle_ticks = 66; + + // How many times to repeat each trial? + let trials = 3; + + // The total time a trial would take, in a perfect unloaded system + let theoretical = (num_steps * work_ticks) + (num_steps * idle_ticks); + + defmt::println!(""); + defmt::println!("Starting UNPRIORITIZED worker trials"); + for _ in 0..trials { + // + // UNPRIORITIZED worker + // + defmt::println!(""); + defmt::println!("Starting unprioritized worker"); + let start = Instant::now(); + for _ in 0..num_steps { + let now = Instant::now(); + while now.elapsed().as_ticks() < work_ticks {} + Timer::after_ticks(idle_ticks).await; + } + let elapsed = start.elapsed().as_ticks(); + defmt::println!( + "Trial complete, theoretical ticks: {=u64}, actual ticks: {=u64}", + theoretical, + elapsed + ); + let ratio = ((elapsed as f32) / (theoretical as f32)) * 100.0; + defmt::println!("Took {=f32}% of ideal time", ratio); + Timer::after_millis(500).await; + } + + Timer::after_secs(1).await; + + defmt::println!(""); + defmt::println!("Starting PRIORITIZED worker trials"); + for _ in 0..trials { + // + // PRIORITIZED worker + // + defmt::println!(""); + defmt::println!("Starting prioritized worker"); + let start = Instant::now(); + // Set the deadline to ~2x the theoretical time. In practice, setting any deadline + // here elevates the current task above all other worker tasks. + Deadline::set_current_task_deadline_after(theoretical * 2).await; + + // Perform the trial + for _ in 0..num_steps { + let now = Instant::now(); + while now.elapsed().as_ticks() < work_ticks {} + Timer::after_ticks(idle_ticks).await; + } + + let elapsed = start.elapsed().as_ticks(); + defmt::println!( + "Trial complete, theoretical ticks: {=u64}, actual ticks: {=u64}", + theoretical, + elapsed + ); + let ratio = ((elapsed as f32) / (theoretical as f32)) * 100.0; + defmt::println!("Took {=f32}% of ideal time", ratio); + + // Unset the deadline, deadlines are not automatically cleared, and if our + // deadline is in the past, then we get very high priority! + Deadline::clear_current_task_deadline().await; + + Timer::after_millis(500).await; + } + + defmt::println!(""); + defmt::println!("Trials Complete."); +} + +#[embassy_executor::task(pool_size = 32)] +async fn load_task(id: u32, ticks_on: u64, ttl_ticks: u64) { + let mut last_print = Instant::now(); + let mut last_tick = last_print; + let mut variance = 0; + let mut max_variance = 0; + loop { + let tgt = last_tick + Duration::from_ticks(ttl_ticks); + assert!(tgt > Instant::now(), "fell too behind!"); + + Timer::at(tgt).await; + let now = Instant::now(); + // How late are we from the target? + let var = now.duration_since(tgt).as_ticks(); + max_variance = max_variance.max(var); + variance += var; + + // blocking work + while now.elapsed().as_ticks() < ticks_on {} + + if last_print.elapsed() >= Duration::from_secs(1) { + defmt::trace!( + "Task {=u32} variance ticks (1s): {=u64}, max: {=u64}, act: {=u64}", + id, + variance, + max_variance, + ticks_on, + ); + max_variance = 0; + variance = 0; + last_print = Instant::now(); + } + + last_tick = tgt; + } +} -- cgit