tcg: rename tcg_current_cpu to tcg_current_rr_cpu

..and make the definition local to cpus. In preparation for MTTCG the
concept of a global tcg_current_cpu will no longer make sense. However
we still need to keep track of it in the single-threaded case to be able
to exit quickly when required.

qemu_cpu_kick_no_halt() moves and becomes qemu_cpu_kick_rr_cpu() to
emphasise its use-case. qemu_cpu_kick now kicks the relevant cpu as
well as qemu_kick_rr_cpu() which will become a no-op in MTTCG.

For the time being the setting of the global exit_request remains.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>

cpu-exec-common.c

@@ -24,7 +24,6 @@
 #include "exec/memory-internal.h"
 
 bool exit_request;
-CPUState *tcg_current_cpu;
 
 /* exit the current TB, but without causing any exception to be raised */
 void cpu_loop_exit_noexc(CPUState *cpu)

cpu-exec.c

@@ -612,7 +612,6 @@ int cpu_exec(CPUState *cpu)
         return EXCP_HALTED;
     }
 
-    atomic_mb_set(&tcg_current_cpu, cpu);
     rcu_read_lock();
 
     if (unlikely(atomic_mb_read(&exit_request))) {
@@ -666,7 +665,5 @@ int cpu_exec(CPUState *cpu)
     /* fail safe : never use current_cpu outside cpu_exec() */
     current_cpu = NULL;
 
-    /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
-    atomic_set(&tcg_current_cpu, NULL);
     return ret;
 }

cpus.c

@@ -780,8 +780,7 @@ void configure_icount(QemuOpts *opts, Error **errp)
  */
 
 static QEMUTimer *tcg_kick_vcpu_timer;
-
+static CPUState *tcg_current_rr_cpu;
-static void qemu_cpu_kick_no_halt(void);
 
 #define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10)
 
@@ -790,10 +789,23 @@ static inline int64_t qemu_tcg_next_kick(void)
     return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
 }
 
+/* Kick the currently round-robin scheduled vCPU */
+static void qemu_cpu_kick_rr_cpu(void)
+{
+    CPUState *cpu;
+    atomic_mb_set(&exit_request, 1);
+    do {
+        cpu = atomic_mb_read(&tcg_current_rr_cpu);
+        if (cpu) {
+            cpu_exit(cpu);
+        }
+    } while (cpu != atomic_mb_read(&tcg_current_rr_cpu));
+}
+
 static void kick_tcg_thread(void *opaque)
 {
     timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
-    qemu_cpu_kick_no_halt();
+    qemu_cpu_kick_rr_cpu();
 }
 
 static void start_tcg_kick_timer(void)
@@ -813,7 +825,6 @@ static void stop_tcg_kick_timer(void)
     }
 }
 
-
 /***********************************************************/
 void hw_error(const char *fmt, ...)
 {
@@ -1324,6 +1335,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
         }
 
         for (; cpu != NULL && !exit_request; cpu = CPU_NEXT(cpu)) {
+            atomic_mb_set(&tcg_current_rr_cpu, cpu);
 
             qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
                               (cpu->singlestep_enabled & SSTEP_NOTIMER) == 0);
@@ -1343,6 +1355,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
             }
 
         } /* for cpu.. */
+        /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
+        atomic_set(&tcg_current_rr_cpu, NULL);
 
         /* Pairs with smp_wmb in qemu_cpu_kick.  */
         atomic_mb_set(&exit_request, 0);
@@ -1421,24 +1435,13 @@ static void qemu_cpu_kick_thread(CPUState *cpu)
 #endif
 }
 
-static void qemu_cpu_kick_no_halt(void)
-{
-    CPUState *cpu;
-    /* Ensure whatever caused the exit has reached the CPU threads before
-     * writing exit_request.
-     */
-    atomic_mb_set(&exit_request, 1);
-    cpu = atomic_mb_read(&tcg_current_cpu);
-    if (cpu) {
-        cpu_exit(cpu);
-    }
-}
-
 void qemu_cpu_kick(CPUState *cpu)
 {
     qemu_cond_broadcast(cpu->halt_cond);
     if (tcg_enabled()) {
-        qemu_cpu_kick_no_halt();
+        cpu_exit(cpu);
+        /* Also ensure current RR cpu is kicked */
+        qemu_cpu_kick_rr_cpu();
     } else {
         if (hax_enabled()) {
             /*
@@ -1486,7 +1489,7 @@ void qemu_mutex_lock_iothread(void)
         atomic_dec(&iothread_requesting_mutex);
     } else {
         if (qemu_mutex_trylock(&qemu_global_mutex)) {
-            qemu_cpu_kick_no_halt();
+            qemu_cpu_kick_rr_cpu();
             qemu_mutex_lock(&qemu_global_mutex);
         }
         atomic_dec(&iothread_requesting_mutex);

include/exec/exec-all.h

@@ -405,7 +405,6 @@ bool memory_region_is_unassigned(MemoryRegion *mr);
 extern int singlestep;
 
 /* cpu-exec.c, accessed with atomic_mb_read/atomic_mb_set */
-extern CPUState *tcg_current_cpu;
 extern bool exit_request;
 
 #endif