[Qemu-devel] [RFC] [PATCHv2] aio / timers pt2: Replace main_loop_tlg with qemu_dummy_timer_ctx

[Alex Bligh]

Currently we use a separate timer list group (main_loop_tlg)
for the main loop. This patch replaces this with a dummy AioContext
used just for timers in the main loop.

Signed-off-by: Alex Bligh <address@hidden>
---
 include/block/aio.h  |    3 +++
 include/qemu/timer.h |    9 ++-------
 main-loop.c          |    2 +-
 qemu-timer.c         |   39 +++++++++++++++++++++++++++++++++------
 4 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/include/block/aio.h b/include/block/aio.h
index b08de19..50a064d 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -81,6 +81,9 @@ typedef struct AioContext {
 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
 typedef int (AioFlushEventNotifierHandler)(EventNotifier *e);
 
+/* Dummy AioContext for main loop timers */
+extern AioContext *qemu_dummy_timer_ctx;
+
 /**
  * aio_context_new: Allocate a new AioContext.
  *
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 716f50b..aac3141 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -58,8 +58,6 @@ typedef struct QEMUTimer {
     int scale;
 } QEMUTimer;
 
-extern QEMUTimerListGroup main_loop_tlg;
-
 /*
  * QEMUClockType
  */
@@ -437,11 +435,8 @@ static inline QEMUTimer *timer_new_tl(QEMUTimerList 
*timer_list,
  *
  * Returns: a pointer to the timer
  */
-static inline QEMUTimer *timer_new(QEMUClockType type, int scale,
-                                   QEMUTimerCB *cb, void *opaque)
-{
-    return timer_new_tl(main_loop_tlg[type], scale, cb, opaque);
-}
+QEMUTimer *timer_new(QEMUClockType type, int scale,
+                     QEMUTimerCB *cb, void *opaque);
 
 /**
  * timer_new_ns:
diff --git a/main-loop.c b/main-loop.c
index 1f24ac1..f1ee0e5 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -479,7 +479,7 @@ int main_loop_wait(int nonblocking)
 
     timeout_ns = qemu_soonest_timeout(timeout_ns,
                                       timerlistgroup_deadline_ns(
-                                          main_loop_tlg));
+                                          qemu_dummy_timer_ctx->tlg));
 
     ret = os_host_main_loop_wait(timeout_ns);
     qemu_iohandler_poll(gpollfds, ret);
diff --git a/qemu-timer.c b/qemu-timer.c
index 0d36a21..dd0b00a 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -54,7 +54,8 @@ typedef struct QEMUClock {
     bool enabled;
 } QEMUClock;
 
-QEMUTimerListGroup main_loop_tlg;
+AioContext *qemu_dummy_timer_ctx;
+
 QEMUClock qemu_clocks[QEMU_CLOCK_MAX];
 
 /* A QEMUTimerList is a list of timers attached to a clock. More
@@ -123,7 +124,6 @@ static void qemu_clock_init(QEMUClockType type)
     clock->last = INT64_MIN;
     QLIST_INIT(&clock->timerlists);
     notifier_list_init(&clock->reset_notifiers);
-    main_loop_tlg[type] = timerlist_new(type, NULL, NULL);
 }
 
 bool qemu_clock_use_for_deadline(QEMUClockType type)
@@ -158,7 +158,7 @@ bool timerlist_has_timers(QEMUTimerList *timer_list)
 bool qemu_clock_has_timers(QEMUClockType type)
 {
     return timerlist_has_timers(
-        main_loop_tlg[type]);
+        qemu_dummy_timer_ctx->tlg[type]);
 }
 
 bool timerlist_expired(QEMUTimerList *timer_list)
@@ -171,7 +171,7 @@ bool timerlist_expired(QEMUTimerList *timer_list)
 bool qemu_clock_expired(QEMUClockType type)
 {
     return timerlist_expired(
-        main_loop_tlg[type]);
+        qemu_dummy_timer_ctx->tlg[type]);
 }
 
 /*
@@ -221,7 +221,7 @@ QEMUClockType timerlist_get_clock(QEMUTimerList *timer_list)
 
 QEMUTimerList *qemu_clock_get_main_loop_timerlist(QEMUClockType type)
 {
-    return main_loop_tlg[type];
+    return qemu_dummy_timer_ctx->tlg[type];
 }
 
 void timerlist_notify(QEMUTimerList *timer_list)
@@ -291,6 +291,19 @@ void timer_init(QEMUTimer *ts,
     ts->scale = scale;
 }
 
+QEMUTimer *timer_new(QEMUClockType type, int scale,
+                     QEMUTimerCB *cb, void *opaque)
+{
+    /* If this assert triggers, this is likely to mean
+     * that a timer is allocated prior to the dummy
+     * timer context being set up
+     */
+    assert(qemu_dummy_timer_ctx);
+
+    return timer_new_tl(qemu_dummy_timer_ctx->tlg[type],
+                        scale, cb, opaque);
+}
+
 void timer_free(QEMUTimer *ts)
 {
     g_free(ts);
@@ -397,7 +410,7 @@ bool timerlist_run_timers(QEMUTimerList *timer_list)
 
 bool qemu_clock_run_timers(QEMUClockType type)
 {
-    return timerlist_run_timers(main_loop_tlg[type]);
+    return timerlist_run_timers(qemu_dummy_timer_ctx->tlg[type]);
 }
 
 void timerlistgroup_init(QEMUTimerListGroup tlg,
@@ -486,6 +499,20 @@ void init_clocks(void)
         qemu_clock_init(type);
     }
 
+    /* Make a dummy context for timers in the main loop.
+     * 
+     * This context should not call the AioContext's
+     * supplied notifier function (which calls
+     * aio_notify) as it needs to call qemu_notify()
+     * instead, as there's nothing actually using the
+     * AioContext. This is a bit of a hack.
+     */
+    qemu_dummy_timer_ctx = aio_context_new();
+    for (type = 0; type < QEMU_CLOCK_MAX; type++) {
+        qemu_dummy_timer_ctx->tlg[type]->notify_cb = NULL;
+        qemu_dummy_timer_ctx->tlg[type]->notify_opaque = NULL;
+    }
+
 #ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
     prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
 #endif
-- 
1.7.9.5