Some scheduler hacks

dcddf43f · Silas Boyd-Wickizer · a4551d12 · dcddf43f
--- a/kernel/sched.cc
+++ b/kernel/sched.cc
@@ -14,6 +14,7 @@
 #include "percpu.hh"
 #include "sperf.hh"
 #include "major.h"
+#include "rnd.hh"

 enum { sched_debug = 0 };
 enum { steal_nonexec = 1 };
@@ -33,14 +34,14 @@ public:
  }

  sched_stat stats_;
+  u64 ncansteal_;
  
 private:
-  struct spinlock lock_;
-  sched_link head_;
-
  void sanity(void);

-  volatile u64 ncansteal_ __mpalign__;
+  struct spinlock lock_ __mpalign__;
+  sched_link head_;
+  volatile bool cansteal_ __mpalign__;
 };
 percpu<schedule> schedule_;

@@ -72,7 +73,8 @@ schedule::enq(proc* p)
  head_.prev->next = entry;
  head_.prev = entry;
  if (cansteal((proc*)entry, true))
-    ncansteal_++;
+    if (ncansteal_++ == 0)
+      cansteal_ = true;
  sanity();
  stats_.enqs++;
 }
@@ -93,7 +95,8 @@ schedule::deq(void)
  entry->next->prev = entry->prev;
  entry->prev->next = entry->next;
  if (cansteal((proc*)entry, true))
-    --ncansteal_;
+    if (--ncansteal_ == 0)
+      cansteal_ = false;
  sanity();
  stats_.deqs++;
  return (proc*)entry;
@@ -102,7 +105,7 @@ schedule::deq(void)
 proc*
 schedule::steal(bool nonexec)
 {
-  if (ncansteal_ == 0 || !tryacquire(&lock_))
+  if (!cansteal_ || !tryacquire(&lock_))
    return nullptr;

  ANON_REGION(__func__, &perfgroup);
@@ -110,7 +113,8 @@ schedule::steal(bool nonexec)
    if (cansteal((proc*)ptr, nonexec)) {
      ptr->next->prev = ptr->prev;
      ptr->prev->next = ptr->next;
-      --ncansteal_;
+      if (--ncansteal_ == 0)
+        cansteal_ = false;
      sanity();
      ++stats_.steals;
      release(&lock_);
@@ -174,12 +178,17 @@ steal(void)
 {
  struct proc *steal;
  int r = 0;
+  u64 s = rnd();

  pushcli();

  for (int nonexec = 0; nonexec < (steal_nonexec ? 2 : 1); nonexec++) { 
-    for (int i = 0; i < NCPU; i++) {
-      steal = schedule_[i].steal(nonexec);
+    for (u64 i = 0; i < NCPU; i++) {
+      u64 k = (s+i) % NCPU;
+      if (k == myid())
+        continue;
+
+      steal = schedule_[k].steal(nonexec);
      if (steal != nullptr) {
        acquire(&steal->lock);
        if (steal->get_state() == RUNNABLE && !steal->cpu_pin &&