Add a uwq member to cpu and only write to it when necessary

84da53b1 · Silas Boyd-Wickizer · e38988a8 · 84da53b1 · 84da53b1 · 84da53b1
--- a/include/cpu.hh
+++ b/include/cpu.hh
@@ -7,6 +7,8 @@ using std::atomic;

 extern atomic<u64> tlbflush_req;

+class uwq;
+
 // Per-CPU state
 struct cpu {
  cpuid_t id;                  // Index into cpus[] below
@@ -20,6 +22,7 @@ struct cpu {
  atomic<u64> tlbflush_done;   // last tlb flush req done on this cpu
  struct proc *prev;           // The previously-running process

+  uwq* uwq __mpalign__;        // Current userspace wq (might be nullptr)
  hwid_t hwid __mpalign__;     // Local APIC ID, accessed by other CPUs

  // Cpu-local storage variables; see below

--- a/kernel/sched.cc
+++ b/kernel/sched.cc
@@ -291,6 +291,9 @@ sched(void)
  mycpu()->proc = next;
  mycpu()->prev = prev;

+  if (mycpu()->uwq != nullptr || next->uwq != nullptr)
+    mycpu()->uwq = next->uwq;
+
  if (prev->get_state() == ZOMBIE)
    mtstop(prev);
  else

--- a/kernel/uwq.cc
+++ b/kernel/uwq.cc
@@ -31,14 +31,11 @@ uwq_trywork(void)
      continue;
    struct cpu *c = &cpus[j];
    
-    // The gc_epoch is for p and uwq
+    // The gc_epoch is for uwq
    scoped_gc_epoch xgc();
    barrier();

-    struct proc *p = c->proc;
-    if (p == nullptr)
-      continue;
-    uwq* uwq = p->uwq;
+    uwq* uwq = c->uwq;
    if (uwq == nullptr)
      continue;