[runtime] Enhancement: Add bounds check to timer resolution

src/rust/runtime/mod.rs

@@ -83,16 +83,21 @@ use ::std::{
         SystemTime,
     },
 };
-use std::pin::Pin;
+use std::{
+    cmp::{
+        max,
+        min,
+    },
+    pin::Pin,
+};
 
 //======================================================================================================================
 // Constants
 //======================================================================================================================
 
-// TODO: Make this more accurate using rdtsc.
-// FIXME: https://github.com/microsoft/demikernel/issues/1226
-const TIMER_RESOLUTION: usize = 64;
-const TIMER_FINER_RESOLUTION: usize = 2;
+const MIN_TIMER_RESOLUTION: usize = 64;
+const MAX_TIMER_RESOLUTION: usize = 1_000_000;
+const FINE_TIMER_RESOLUTION: usize = 2;
 
 //======================================================================================================================
 // Structures
@@ -158,7 +163,7 @@ impl SharedDemiRuntime {
                 rdtscp
             },
             last_time: Instant::now(),
-            timer_resolution: TIMER_RESOLUTION,
+            timer_resolution: MIN_TIMER_RESOLUTION,
             completed_tasks: HashMap::<QToken, (QDesc, OperationResult)>::new(),
         }))
     }
@@ -371,7 +376,7 @@ impl SharedDemiRuntime {
     fn run_next(&mut self, timeout: Duration) -> Option<(QToken, QDesc, OperationResult)> {
         let iterations: usize = match timeout {
             timeout if timeout.as_secs() > 0 => self.timer_resolution,
-            _ => TIMER_FINER_RESOLUTION,
+            _ => FINE_TIMER_RESOLUTION,
         };
         if let Some(boxed_task) = self.scheduler.get_next_completed_task(iterations) {
             // Perform bookkeeping for the completed and removed task.
@@ -565,12 +570,12 @@ impl SharedDemiRuntime {
             return;
         }
 
-        let cycles_per_quanta: usize = cycles_per_second / TIMER_RESOLUTION;
+        let cycles_per_quanta: usize = cycles_per_second / MIN_TIMER_RESOLUTION;
         if cycles_per_quanta == 0 {
             return;
         }
 
-        self.timer_resolution = cycles_per_quanta;
+        self.timer_resolution = max(MIN_TIMER_RESOLUTION, min(MAX_TIMER_RESOLUTION, cycles_per_quanta));
         trace!("Adjusted timer resolution to: {:?}", self.timer_resolution);
         self.last_tsc = curr_tsc;
         self.last_time = now;
@@ -642,7 +647,7 @@ impl Default for SharedDemiRuntime {
                 tsc
             },
             last_time: Instant::now(),
-            timer_resolution: TIMER_RESOLUTION,
+            timer_resolution: MIN_TIMER_RESOLUTION,
             completed_tasks: HashMap::<QToken, (QDesc, OperationResult)>::new(),
         }))
     }