[Qemu-devel] [PATCH v4 07/12] linux-user: Rework exclusive operation mechanism

[Sergey Fedorov]

From: Sergey Fedorov <serge.f...@gmail.com>

A single variable 'pending_cpus' was used for both counting currently
running CPUs and for signalling the pending exclusive operation request.

To prepare for supporting operations which requires a quiescent state,
like translation buffer flush, it is useful to keep a counter of
currently running CPUs always up to date.

Use a separate variable 'tcg_pending_threads' to count for currently
running CPUs and a separate variable 'exclusive_pending' to indicate
that there's an exclusive operation pending.

Signed-off-by: Sergey Fedorov <serge.f...@gmail.com>
Signed-off-by: Sergey Fedorov <sergey.fedo...@linaro.org>
Reviewed-by: Alex Bennée <alex.ben...@linaro.org>

---
Changes in v2:
 - Rename 'tcg_pending_cpus' to 'tcg_pending_threads'
---
 linux-user/main.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index bdbda693cc5f..5ff0b20bad89 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -112,7 +112,8 @@ static QemuMutex cpu_list_mutex;
 static QemuMutex exclusive_lock;
 static QemuCond exclusive_cond;
 static QemuCond exclusive_resume;
-static int pending_cpus;
+static bool exclusive_pending;
+static int tcg_pending_threads;
 
 void qemu_init_cpu_loop(void)
 {
@@ -142,7 +143,8 @@ void fork_end(int child)
                 QTAILQ_REMOVE(&cpus, cpu, node);
             }
         }
-        pending_cpus = 0;
+        tcg_pending_threads = 0;
+        exclusive_pending = false;
         qemu_mutex_init(&exclusive_lock);
         qemu_mutex_init(&cpu_list_mutex);
         qemu_cond_init(&exclusive_cond);
@@ -159,7 +161,7 @@ void fork_end(int child)
    must be held.  */
 static inline void exclusive_idle(void)
 {
-    while (pending_cpus) {
+    while (exclusive_pending) {
         qemu_cond_wait(&exclusive_resume, &exclusive_lock);
     }
 }
@@ -173,15 +175,14 @@ static inline void start_exclusive(void)
     qemu_mutex_lock(&exclusive_lock);
     exclusive_idle();
 
-    pending_cpus = 1;
+    exclusive_pending = true;
     /* Make all other cpus stop executing.  */
     CPU_FOREACH(other_cpu) {
         if (other_cpu->running) {
-            pending_cpus++;
             cpu_exit(other_cpu);
         }
     }
-    if (pending_cpus > 1) {
+    while (tcg_pending_threads) {
         qemu_cond_wait(&exclusive_cond, &exclusive_lock);
     }
 }
@@ -189,7 +190,7 @@ static inline void start_exclusive(void)
 /* Finish an exclusive operation.  */
 static inline void __attribute__((unused)) end_exclusive(void)
 {
-    pending_cpus = 0;
+    exclusive_pending = false;
     qemu_cond_broadcast(&exclusive_resume);
     qemu_mutex_unlock(&exclusive_lock);
 }
@@ -200,6 +201,7 @@ static inline void cpu_exec_start(CPUState *cpu)
     qemu_mutex_lock(&exclusive_lock);
     exclusive_idle();
     cpu->running = true;
+    tcg_pending_threads++;
     qemu_mutex_unlock(&exclusive_lock);
 }
 
@@ -208,11 +210,9 @@ static inline void cpu_exec_end(CPUState *cpu)
 {
     qemu_mutex_lock(&exclusive_lock);
     cpu->running = false;
-    if (pending_cpus > 1) {
-        pending_cpus--;
-        if (pending_cpus == 1) {
-            qemu_cond_signal(&exclusive_cond);
-        }
+    tcg_pending_threads--;
+    if (!tcg_pending_threads) {
+        qemu_cond_signal(&exclusive_cond);
     }
     exclusive_idle();
     qemu_mutex_unlock(&exclusive_lock);
-- 
2.9.1