some comment changes

1 files changed, 6 insertions, 7 deletions

diff --git a/spinlock.c b/spinlock.c
index 2e604b7..f814632 100644
--- a/spinlock.c
+++ b/spinlock.c
@@ -51,10 +51,9 @@ acquire(struct spinlock *lock)
   while(cmpxchg(0, 1, &lock->locked) == 1)
     ;
 
-  // Now that lock is acquired, make sure 
-  // we wait for all pending writes from other
-  // processors.
-  cpuid(0, 0, 0, 0, 0);  // memory barrier
+  // Serialize instructions: now that lock is acquired, make sure 
+  // we wait for all pending writes from other processors.
+  cpuid(0, 0, 0, 0, 0);  // memory barrier (see Ch 7 of IA-32 manual, vol 3)
   
   // Record info about lock acquisition for debugging.
   // The +10 is only so that we can tell the difference
@@ -74,9 +73,9 @@ release(struct spinlock *lock)
   lock->pcs[0] = 0;
   lock->cpu = 0xffffffff;
   
-  // Before unlocking the lock, make sure to flush
-  // any pending memory writes from this processor.
-  cpuid(0, 0, 0, 0, 0);  // memory barrier
+  // Serialize instructions: before unlocking the lock, make sure
+  // to flush any pending memory writes from this processor.
+  cpuid(0, 0, 0, 0, 0);  // memory barrier (see Ch 7 of IA-32 manual, vol 3)
 
   lock->locked = 0;
   if(--cpus[cpu()].nlock == 0)