[Qemu-devel] [RFC] [PATCHv6 14/16] aio / timers: Use all timerlists in icount warp calculations

[Alex Bligh]

Notify all timerlists derived from vm_clock in icount warp
calculations.

When calculating timer delay based on vm_clock deadline, use
all timerlists.

For compatibility, maintain an apparent bug where when using
icount, if no vm_clock timer was set, qemu_clock_deadline
would return INT32_MAX and always set an icount clock expiry
about 2 seconds ahead.

NB: thread safety - when different timerlists sit on different
threads, this will need some locking.

Signed-off-by: Alex Bligh <address@hidden>
---
 cpus.c               |   44 ++++++++++++++++++++++++++++++++++++--------
 include/qemu/timer.h |    1 +
 qemu-timer.c         |   16 ++++++++++++++++
 3 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/cpus.c b/cpus.c
index 0f65e76..55b9550 100644
--- a/cpus.c
+++ b/cpus.c
@@ -262,7 +262,7 @@ static void icount_warp_rt(void *opaque)
             qemu_icount_bias += MIN(warp_delta, delta);
         }
         if (qemu_clock_expired(vm_clock)) {
-            qemu_notify_event();
+            qemu_clock_notify(vm_clock);
         }
     }
     vm_clock_warp_start = -1;
@@ -279,7 +279,7 @@ void qtest_clock_warp(int64_t dest)
         qemu_run_timers(vm_clock);
         clock = qemu_get_clock_ns(vm_clock);
     }
-    qemu_notify_event();
+    qemu_clock_notify(vm_clock);
 }
 
 void qemu_clock_warp(QEMUClock *clock)
@@ -314,7 +314,18 @@ void qemu_clock_warp(QEMUClock *clock)
     }
 
     vm_clock_warp_start = qemu_get_clock_ns(rt_clock);
-    deadline = qemu_clock_deadline(vm_clock);
+    /* We want to use the earliest deadline from ALL vm_clocks */
+    deadline = qemu_clock_deadline_ns_all(vm_clock);
+
+    /* Maintain prior (possibly buggy) behaviour where if no deadline
+     * was set (as there is no vm_clock timer) or it is more than
+     * INT32_MAX nanoseconds ahead, we still use INT32_MAX
+     * nanoseconds.
+     */
+    if ((deadline < 0) || (deadline > INT32_MAX)) {
+        deadline = INT32_MAX;
+    }
+
     if (deadline > 0) {
         /*
          * Ensure the vm_clock proceeds even when the virtual CPU goes to
@@ -333,8 +344,8 @@ void qemu_clock_warp(QEMUClock *clock)
          * packets continuously instead of every 100ms.
          */
         qemu_mod_timer(icount_warp_timer, vm_clock_warp_start + deadline);
-    } else {
-        qemu_notify_event();
+    } else if (deadline == 0) {
+        qemu_clock_notify(vm_clock);
     }
 }
 
@@ -866,8 +877,13 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
 
     while (1) {
         tcg_exec_all();
-        if (use_icount && qemu_clock_deadline(vm_clock) <= 0) {
-            qemu_notify_event();
+
+        if (use_icount) {
+            int64_t deadline = qemu_clock_deadline_ns_all(vm_clock);
+
+            if (deadline == 0) {
+                qemu_clock_notify(vm_clock);
+            }
         }
         qemu_tcg_wait_io_event();
     }
@@ -1145,11 +1161,23 @@ static int tcg_cpu_exec(CPUArchState *env)
 #endif
     if (use_icount) {
         int64_t count;
+        int64_t deadline;
         int decr;
         qemu_icount -= (env->icount_decr.u16.low + env->icount_extra);
         env->icount_decr.u16.low = 0;
         env->icount_extra = 0;
-        count = qemu_icount_round(qemu_clock_deadline(vm_clock));
+        deadline = qemu_clock_deadline_ns_all(vm_clock);
+
+        /* Maintain prior (possibly buggy) behaviour where if no deadline
+         * was set (as there is no vm_clock timer) or it is more than
+         * INT32_MAX nanoseconds ahead, we still use INT32_MAX
+         * nanoseconds.
+         */
+        if ((deadline < 0) || (deadline > INT32_MAX)) {
+            deadline = INT32_MAX;
+        }
+
+        count = qemu_icount_round(deadline);
         qemu_icount += count;
         decr = (count > 0xffff) ? 0xffff : count;
         count -= decr;
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index d3d4701..b6e5efd 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -60,6 +60,7 @@ int64_t qemu_clock_has_timers(QEMUClock *clock);
 int64_t qemu_clock_expired(QEMUClock *clock);
 int64_t qemu_clock_deadline(QEMUClock *clock);
 int64_t qemu_clock_deadline_ns(QEMUClock *clock);
+int64_t qemu_clock_deadline_ns_all(QEMUClock *clock);
 bool qemu_clock_use_for_deadline(QEMUClock *clock);
 QEMUTimerList *qemu_clock_get_default_timerlist(QEMUClock *clock);
 void qemu_clock_notify(QEMUClock *clock);
diff --git a/qemu-timer.c b/qemu-timer.c
index 5f65455..a7ef047 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -389,6 +389,22 @@ int64_t qemu_clock_deadline_ns(QEMUClock *clock)
     return timerlist_deadline_ns(clock->default_timerlist);
 }
 
+/* Calculate the soonest deadline across all timerlists attached
+ * to the clock. This is used for the icount timeout so we
+ * ignore whether or not the clock should be used in deadline
+ * calculations.
+ */
+int64_t qemu_clock_deadline_ns_all(QEMUClock *clock)
+{
+    int64_t deadline = -1;
+    QEMUTimerList *tl;
+    QLIST_FOREACH(tl, &clock->timerlists, list) {
+        deadline = qemu_soonest_timeout(deadline,
+                                        timerlist_deadline_ns(tl));
+    }
+    return deadline;
+}
+
 QEMUClock *timerlist_get_clock(QEMUTimerList *tl)
 {
     return tl->clock;
-- 
1.7.9.5