[Qemu-devel] [RFC v3 14/19] tcg: remove global exit_request

[Alex Bennée]

The only remaining use of the global exit_request flag is now to ensure
we exit the run_loop when we first start to process pending work. This
is just as easily done by setting the first_cpu->exit_request flag.

We lightly re-factor the main vCPU thread to ensure cpu->exit_requests
cause us to exit the main loop and process any IO requests that might
come along.

Signed-off-by: Alex Bennée <address@hidden>
---
 cpu-exec-common.c       |  2 --
 cpu-exec.c              | 10 +++-------
 cpus.c                  | 35 +++++++++++++++++++++++------------
 include/exec/exec-all.h |  2 --
 4 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/cpu-exec-common.c b/cpu-exec-common.c
index f42d24a..1b4fb53 100644
--- a/cpu-exec-common.c
+++ b/cpu-exec-common.c
@@ -23,8 +23,6 @@
 #include "exec/exec-all.h"
 #include "exec/memory-internal.h"
 
-bool exit_request;
-
 /* exit the current TB from a signal handler. The host registers are
    restored in a state compatible with the CPU emulator
  */
diff --git a/cpu-exec.c b/cpu-exec.c
index 68e804b..1613c63 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -541,9 +541,8 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, 
TranslationBlock *tb,
         /* Something asked us to stop executing
          * chained TBs; just continue round the main
          * loop. Whatever requested the exit will also
-         * have set something else (eg exit_request or
-         * interrupt_request) which we will handle
-         * next time around the loop.  But we need to
+         * have set something else (eg interrupt_request) which we
+         * will handle next time around the loop.  But we need to
          * ensure the tcg_exit_req read in generated code
          * comes before the next read of cpu->exit_request
          * or cpu->interrupt_request.
@@ -594,15 +593,12 @@ int cpu_exec(CPUState *cpu)
     current_cpu = cpu;
 
     if (cpu_handle_halt(cpu)) {
+        cpu->exit_request = true;
         return EXCP_HALTED;
     }
 
     rcu_read_lock();
 
-    if (unlikely(atomic_mb_read(&exit_request))) {
-        cpu->exit_request = 1;
-    }
-
     cc->cpu_exec_enter(cpu);
 
     /* Calculate difference between guest clock and host clock.
diff --git a/cpus.c b/cpus.c
index a139ad3..a84f02c 100644
--- a/cpus.c
+++ b/cpus.c
@@ -1169,6 +1169,18 @@ static int64_t tcg_get_icount_limit(void)
     }
 }
 
+static void handle_icount_deadline(void)
+{
+    if (use_icount) {
+        int64_t deadline =
+            qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
+
+        if (deadline == 0) {
+            qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
+        }
+    }
+}
+
 static int tcg_cpu_exec(CPUState *cpu)
 {
     int ret;
@@ -1276,11 +1288,11 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
         timer_mod(kick_timer, TCG_KICK_FREQ);
     }
 
-    /* process any pending work */
-    atomic_mb_set(&exit_request, 1);
-
     cpu = first_cpu;
 
+    /* process any pending work */
+    atomic_mb_set(&cpu->exit_request, 1);
+
     while (1) {
         /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */
         qemu_account_warp_timer();
@@ -1289,7 +1301,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
             cpu = first_cpu;
         }
 
-        for (; cpu != NULL && !exit_request; cpu = CPU_NEXT(cpu)) {
+        while (cpu && !cpu->exit_request) {
             atomic_mb_set(&tcg_current_rr_cpu, cpu);
 
             qemu_clock_enable(QEMU_CLOCK_VIRTUAL,
@@ -1303,22 +1315,21 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
                 }
             } else if (cpu->stop || cpu->stopped) {
                 break;
+            } else if (cpu->exit_request) {
+                break;
             }
 
+            cpu = CPU_NEXT(cpu);
         } /* 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);
+        if (cpu && cpu->exit_request) {
+            atomic_mb_set(&cpu->exit_request, 0);
+        }
 
-        if (use_icount) {
-            int64_t deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
+        handle_icount_deadline();
 
-            if (deadline == 0) {
-                qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
-            }
-        }
         qemu_tcg_wait_io_event(QTAILQ_FIRST(&cpus));
     }
 
diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 31f4c38..7919aac 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -405,6 +405,4 @@ bool memory_region_is_unassigned(MemoryRegion *mr);
 /* vl.c */
 extern int singlestep;
 
-extern bool exit_request;
-
 #endif
-- 
2.7.4