From 47cdb5f0962aee617a1fe448b8d50fe1d3a3e545 Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Wed, 2 Sep 2020 17:17:15 -0400
Subject: [PATCH] wfi to save CPU time on Athena
---
kernel/proc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/proc.c b/kernel/proc.c
index 58a8a0b..4354ec5 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -454,6 +454,7 @@ scheduler(void)
// processes are waiting.
intr_on();
+ int found = 0;
for(p = proc; p < &proc[NPROC]; p++) {
acquire(&p->lock);
if(p->state == RUNNABLE) {
@@ -467,9 +468,14 @@ scheduler(void)
// Process is done running for now.
// It should have changed its p->state before coming back.
c->proc = 0;
+ found = 1;
}
release(&p->lock);
}
+ if(found == 0) {
+ intr_on();
+ asm volatile("wfi");
+ }
}
}