[Qemu-devel] [PATCH v4 3/5] icount: decouple warp calls

[Pavel Dovgalyuk]

qemu_clock_warp function is called to update virtual clock when CPU
is sleeping. This function includes replay checkpoint to make execution
deterministic in icount mode.
Record/replay module flushes async event queue at checkpoints.
Some of the events (e.g., block devices operations) include interaction
with hardware. E.g., APIC polled by block devices sets one of IRQ flags.
Flag to be set depends on currently executed thread (CPU or iothread).
Therefore in replay mode we have to process the checkpoints in the same thread
as they were recorded.
qemu_clock_warp function (and its checkpoint) may be called from different
thread. This patch decouples two different execution cases of this function:
call when CPU is sleeping from iothread and call from cpu thread to update
virtual clock.
First task is performed by qemu_start_warp_timer function. It sets warp
timer event to the moment of nearest pending virtual timer.
Second function (qemu_account_warp_timer) is called from cpu thread
before execution of the code. It advances virtual clock by adding the length
of period while CPU was sleeping.

Signed-off-by: Pavel Dovgalyuk <address@hidden>
---
 cpus.c                  |   53 +++++++++++++++++++++++++++--------------------
 include/qemu/timer.h    |   14 +++++++++---
 include/sysemu/replay.h |    3 ++-
 main-loop.c             |    2 +-
 qemu-timer.c            |    4 +++-
 stubs/clock-warp.c      |    2 +-
 6 files changed, 48 insertions(+), 30 deletions(-)

diff --git a/cpus.c b/cpus.c
index 85d0f87..3ab9e04 100644
--- a/cpus.c
+++ b/cpus.c
@@ -373,6 +373,7 @@ static void icount_warp_rt(void)
 static void icount_dummy_timer(void *opaque)
 {
     (void)opaque;
+    icount_warp_rt();
 }
 
 void qtest_clock_warp(int64_t dest)
@@ -396,17 +397,12 @@ void qtest_clock_warp(int64_t dest)
     qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
 }
 
-void qemu_clock_warp(QEMUClockType type)
+void qemu_start_warp_timer(void)
 {
     int64_t clock;
     int64_t deadline;
 
-    /*
-     * There are too many global variables to make the "warp" behavior
-     * applicable to other clocks.  But a clock argument removes the
-     * need for if statements all over the place.
-     */
-    if (type != QEMU_CLOCK_VIRTUAL || !use_icount) {
+    if (!use_icount) {
         return;
     }
 
@@ -418,29 +414,17 @@ void qemu_clock_warp(QEMUClockType type)
     }
 
     /* warp clock deterministically in record/replay mode */
-    if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP)) {
+    if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_START)) {
         return;
     }
 
-    if (icount_sleep) {
-        /*
-         * If the CPUs have been sleeping, advance QEMU_CLOCK_VIRTUAL timer 
now.
-         * This ensures that the deadline for the timer is computed correctly
-         * below.
-         * This also makes sure that the insn counter is synchronized before
-         * the CPU starts running, in case the CPU is woken by an event other
-         * than the earliest QEMU_CLOCK_VIRTUAL timer.
-         */
-        icount_warp_rt();
-        timer_del(icount_warp_timer);
-    }
     if (!all_cpu_threads_idle()) {
         return;
     }
 
     if (qtest_enabled()) {
         /* When testing, qtest commands advance icount.  */
-       return;
+        return;
     }
 
     /* We want to use the earliest deadline from ALL vm_clocks */
@@ -496,6 +480,31 @@ void qemu_clock_warp(QEMUClockType type)
     }
 }
 
+void qemu_account_warp_timer(void)
+{
+    int64_t clock;
+    int64_t warp_delta;
+
+    if (!use_icount || !icount_sleep) {
+        return;
+    }
+
+    /* Nothing to do if the VM is stopped: QEMU_CLOCK_VIRTUAL timers
+     * do not fire, so computing the deadline does not make sense.
+     */
+    if (!runstate_is_running()) {
+        return;
+    }
+
+    /* warp clock deterministically in record/replay mode */
+    if (!replay_checkpoint(CHECKPOINT_CLOCK_WARP_ACCOUNT)) {
+        return;
+    }
+
+    timer_del(icount_warp_timer);
+    icount_warp_rt();
+}
+
 static bool icount_state_needed(void *opaque)
 {
     return use_icount;
@@ -1496,7 +1505,7 @@ static void tcg_exec_all(void)
     int r;
 
     /* Account partial waits to QEMU_CLOCK_VIRTUAL.  */
-    qemu_clock_warp(QEMU_CLOCK_VIRTUAL);
+    qemu_account_warp_timer();
 
     if (next_cpu == NULL) {
         next_cpu = first_cpu;
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index d0946cb..21ffec6 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -210,12 +210,18 @@ void qemu_clock_notify(QEMUClockType type);
 void qemu_clock_enable(QEMUClockType type, bool enabled);
 
 /**
- * qemu_clock_warp:
- * @type: the clock type
+ * qemu_start_warp_timer:
+ *
+ * Starts a timer for virtual clock update
+ */
+void qemu_start_warp_timer(void);
+
+/**
+ * qemu_account_warp_timer:
  *
- * Warp a clock to a new value
+ * Updates virtual clock for the time CPU was sleeping
  */
-void qemu_clock_warp(QEMUClockType type);
+void qemu_account_warp_timer(void);
 
 /**
  * qemu_clock_register_reset_notifier:
diff --git a/include/sysemu/replay.h b/include/sysemu/replay.h
index 4763e56..6c332e5 100644
--- a/include/sysemu/replay.h
+++ b/include/sysemu/replay.h
@@ -27,7 +27,8 @@ typedef enum ReplayClockKind ReplayClockKind;
 
 /* IDs of the checkpoints */
 enum ReplayCheckpoint {
-    CHECKPOINT_CLOCK_WARP,
+    CHECKPOINT_CLOCK_WARP_START,
+    CHECKPOINT_CLOCK_WARP_ACCOUNT,
     CHECKPOINT_RESET_REQUESTED,
     CHECKPOINT_SUSPEND_REQUESTED,
     CHECKPOINT_CLOCK_VIRTUAL,
diff --git a/main-loop.c b/main-loop.c
index 19beae7..3a7f4cd 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -509,7 +509,7 @@ int main_loop_wait(int nonblocking)
 
     /* CPU thread can infinitely wait for event after
        missing the warp */
-    qemu_clock_warp(QEMU_CLOCK_VIRTUAL);
+    qemu_start_warp_timer();
     qemu_clock_run_all_timers();
 
     return ret;
diff --git a/qemu-timer.c b/qemu-timer.c
index e98ecc9..4441fe6 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -394,7 +394,9 @@ static bool timer_mod_ns_locked(QEMUTimerList *timer_list,
 static void timerlist_rearm(QEMUTimerList *timer_list)
 {
     /* Interrupt execution to force deadline recalculation.  */
-    qemu_clock_warp(timer_list->clock->type);
+    if (timer_list->clock->type == QEMU_CLOCK_VIRTUAL) {
+        qemu_start_warp_timer();
+    }
     timerlist_notify(timer_list);
 }
 
diff --git a/stubs/clock-warp.c b/stubs/clock-warp.c
index 5ae32b9..8acb58a 100644
--- a/stubs/clock-warp.c
+++ b/stubs/clock-warp.c
@@ -2,7 +2,7 @@
 #include "qemu-common.h"
 #include "qemu/timer.h"
 
-void qemu_clock_warp(QEMUClockType type)
+void qemu_start_warp_timer(void)
 {
 }