Implement priority inheritance

Signed-off-by: Klimenty Tsoutsman <klim@tsoutsman.com>
tsoutsman · Sep 8, 2023 · 618b5ce · 618b5ce
1 parent 8917875
commit 618b5ce
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Showing 5 changed files with 43 additions and 75 deletions.
diff --git a/kernel/scheduler/src/lib.rs b/kernel/scheduler/src/lib.rs
@@ -16,8 +16,8 @@
 
 use interrupts::{self, CPU_LOCAL_TIMER_IRQ, interrupt_handler, eoi, EoiBehaviour};
 
-/// A re-export of [`task::schedule()`] for convenience and legacy compatibility.
-pub use task::scheduler::{priority, schedule, set_priority};
+/// Re-exports for convenience and legacy compatibility.
+pub use task::scheduler::{inherit_priority, priority, schedule, set_priority};
 
 
 /// Initializes the scheduler on this system using the policy set at compiler time.

diff --git a/kernel/scheduler_epoch/src/lib.rs b/kernel/scheduler_epoch/src/lib.rs
@@ -184,13 +184,6 @@ impl task::scheduler::PriorityScheduler for Scheduler {
         }
         None
     }
-
-    fn inherit_priority(
-        &mut self,
-        _task: &TaskRef,
-    ) -> task::scheduler::PriorityInheritanceGuard<'_> {
-        todo!()
-    }
 }
 
 #[derive(Debug, Clone)]

diff --git a/kernel/scheduler_priority/src/lib.rs b/kernel/scheduler_priority/src/lib.rs
@@ -110,13 +110,6 @@ impl task::scheduler::PriorityScheduler for Scheduler {
         }
         None
     }
-
-    fn inherit_priority(
-        &mut self,
-        task: &TaskRef,
-    ) -> task::scheduler::PriorityInheritanceGuard<'_> {
-        todo!()
-    }
 }
 
 #[derive(Clone, Debug, Eq)]

diff --git a/kernel/task/src/lib.rs b/kernel/task/src/lib.rs
@@ -26,6 +26,7 @@
 #![no_std]
 #![feature(negative_impls)]
 #![feature(thread_local)]
+#![feature(let_chains)]
 
 extern crate alloc;
 

diff --git a/kernel/task/src/scheduler.rs b/kernel/task/src/scheduler.rs
@@ -187,21 +187,6 @@ pub trait PriorityScheduler {
 
     /// Gets the priority of the given task.
     fn priority(&mut self, task: &TaskRef) -> Option<u8>;
-
-    fn inherit_priority(&mut self, task: &TaskRef) -> PriorityInheritanceGuard<'_>;
-}
-
-/// Lowers the task's priority to its previous value when dropped.
-pub struct PriorityInheritanceGuard<'a> {
-    inner: Option<(&'a TaskRef, u8)>,
-}
-
-impl<'a> Drop for PriorityInheritanceGuard<'a> {
-    fn drop(&mut self) {
-        if let Some((task, priority)) = self.inner {
-            set_priority(task, priority);
-        }
-    }
 }
 
 /// Returns the priority of the given task.
@@ -246,47 +231,43 @@ pub fn busyness(cpu_id: CpuId) -> Option<usize> {
     None
 }
 
-// /// Modifies the given task's priority to be the maximum of its priority and
-// the /// current task's priority.
-// ///
-// /// Returns a guard which reverts the change when dropped.
-// pub fn inherit_priority(task: &TaskRef) -> PriorityInheritanceGuard<'_> {
-//     let current_task = task::get_my_current_task().unwrap();
-
-//     let mut current_priority = None;
-//     let mut other_priority = None;
-
-//     'outer: for (core, run_queue) in RUNQUEUES.iter() {
-//         for epoch_task in run_queue.read().iter() {
-//             if epoch_task.task == current_task {
-//                 current_priority = Some(epoch_task.priority);
-//                 if other_priority.is_some() {
-//                     break 'outer;
-//                 }
-//             } else if &epoch_task.task == task {
-//                 other_priority = Some((core, epoch_task.priority));
-//                 if current_priority.is_some() {
-//                     break 'outer;
-//                 }
-//             }
-//         }
-//     }
-
-//     if let (Some(current_priority), Some((core, other_priority))) =
-//         (current_priority, other_priority) && current_priority >
-// other_priority     {
-//         // NOTE: This assumes no task migration.
-//         debug_assert!(RUNQUEUES.get(core).unwrap().write().set_priority(task,
-// current_priority));     }
-
-//     PriorityInheritanceGuard {
-//         inner: if let (Some(current_priority), Some((_, other_priority))) =
-//             (current_priority, other_priority)
-//             && current_priority > other_priority
-//         {
-//             Some((task, other_priority))
-//         } else {
-//             None
-//         },
-//     }
-// }
+/// Modifies the given task's priority to be the maximum of its priority and the
+/// current task's priority.
+///
+/// Returns a guard which reverts the change when dropped.
+pub fn inherit_priority(task: &TaskRef) -> PriorityInheritanceGuard<'_> {
+    let current_task = super::get_my_current_task().unwrap();
+
+    let current_priority = priority(&current_task);
+    let other_priority = priority(task);
+
+    if let (Some(current_priority), Some(other_priority)) =
+        (current_priority, other_priority) && current_priority > other_priority
+    {
+        set_priority(task, current_priority);
+    }
+
+    PriorityInheritanceGuard {
+        inner: if let (Some(current_priority), Some(other_priority)) =
+            (current_priority, other_priority)
+            && current_priority > other_priority
+        {
+            Some((task, other_priority))
+        } else {
+            None
+        },
+    }
+}
+
+/// Lowers the task's priority to its previous value when dropped.
+pub struct PriorityInheritanceGuard<'a> {
+    inner: Option<(&'a TaskRef, u8)>,
+}
+
+impl<'a> Drop for PriorityInheritanceGuard<'a> {
+    fn drop(&mut self) {
+        if let Some((task, priority)) = self.inner {
+            set_priority(task, priority);
+        }
+    }
+}