[Qemu-devel] [RFC v4 20/28] cpus: tweak sleeping and safe_work rules for MTTCG

[Alex Bennée]

Once TCG gains the ability to sleep individual threads we need to make
sure they don't sleep when safe work is pending as all threads need to
go through the process_queued_work function. Also if we have multiple
threads wait_for_safe_work can now sleep without deadlocking.

Signed-off-by: Alex Bennée <address@hidden>

---
v4
  - new for v4, ontop of async-safe-work-v5
---
 cpu-exec-common.c | 15 ++++++++++++++-
 cpus.c            |  2 +-
 include/qom/cpu.h |  8 ++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/cpu-exec-common.c b/cpu-exec-common.c
index e29cf6d..84cb789 100644
--- a/cpu-exec-common.c
+++ b/cpu-exec-common.c
@@ -83,6 +83,18 @@ QemuCond qemu_exclusive_cond;
 
 static int safe_work_pending;
 
+/* No vCPUs can sleep while there is safe work pending as we need
+ * everything to finish up in process_cpu_work.
+ */
+bool cpu_has_queued_work(CPUState *cpu)
+{
+    if (cpu->queued_work || atomic_mb_read(&safe_work_pending) > 0) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
 #ifdef CONFIG_USER_ONLY
 #define can_wait_for_safe() (1)
 #else
@@ -91,7 +103,8 @@ static int safe_work_pending;
  * all vCPUs are in the same thread. This will change for MTTCG
  * however.
  */
-#define can_wait_for_safe() (0)
+extern int smp_cpus;
+#define can_wait_for_safe() (mttcg_enabled && smp_cpus > 1)
 #endif
 
 void wait_safe_cpu_work(void)
diff --git a/cpus.c b/cpus.c
index 8a40a08..4fc5e4c 100644
--- a/cpus.c
+++ b/cpus.c
@@ -88,7 +88,7 @@ bool cpu_is_stopped(CPUState *cpu)
 
 static bool cpu_thread_is_idle(CPUState *cpu)
 {
-    if (cpu->stop || cpu->queued_work) {
+    if (cpu->stop || cpu_has_queued_work(cpu)) {
         return false;
     }
     if (cpu_is_stopped(cpu)) {
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 5ecbd29..d0db846 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -661,6 +661,14 @@ void async_run_on_cpu(CPUState *cpu, run_on_cpu_func func, 
void *data);
 void async_safe_run_on_cpu(CPUState *cpu, run_on_cpu_func func, void *data);
 
 /**
+ * cpu_has_queued_work:
+ * @cpu: The vCPU to check
+ *
+ * Returns true if there is *_run_on_cpu work to be done.
+ */
+bool cpu_has_queued_work(CPUState *cpu);
+
+/**
  * qemu_get_cpu:
  * @index: The address@hidden value of the CPU to obtain.
  *
-- 
2.7.4