[Qemu-devel] [RFC PATCH v6 13/14] rexec: synchronize icount on the next event.

[fred . konrad]

From: KONRAD Frederic <address@hidden>

We don't want to warp on host clock as it is not deterministic for replay.
So this patch warp icount on the next QEMU_VIRTUAL_CLOCK event if reverse
execution is enabled.

The normal behaviour is kept when reverse execution is disabled.

Signed-off-by: KONRAD Frederic <address@hidden>
---
 cpus.c                         | 19 +++++++++++++++++--
 include/qemu/timer.h           |  8 ++++++++
 include/reverse-execution.h    |  2 ++
 main-loop.c                    | 10 ++++++++++
 stubs/Makefile.objs            |  1 +
 stubs/cpu-get-icount.c         |  8 ++++++++
 stubs/reverse-execution-stub.c | 32 ++++++++++++++++++++++++++++++++
 7 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 stubs/reverse-execution-stub.c

diff --git a/cpus.c b/cpus.c
index f812564..740c6e5 100644
--- a/cpus.c
+++ b/cpus.c
@@ -321,8 +321,10 @@ static int64_t qemu_icount_round(int64_t count)
     return (count + (1 << icount_time_shift) - 1) >> icount_time_shift;
 }
 
-static void icount_warp_rt(void *opaque)
+void icount_warp_rt(void *opaque)
 {
+    int64_t next_vm_deadline = -1;
+
     /* The icount_warp_timer is rescheduled soon after vm_clock_warp_start
      * changes from -1 to another value, so the race here is okay.
      */
@@ -330,6 +332,13 @@ static void icount_warp_rt(void *opaque)
         return;
     }
 
+    if (rexec_is_enabled()) {
+        /*
+         * We need this because the standard warp_delta is not deterministic.
+         */
+        next_vm_deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
+    }
+
     seqlock_write_lock(&timers_state.vm_clock_seqlock);
     if (runstate_is_running()) {
         int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
@@ -346,7 +355,13 @@ static void icount_warp_rt(void *opaque)
             int64_t delta = cur_time - cur_icount;
             warp_delta = MIN(warp_delta, delta);
         }
-        timers_state.qemu_icount_bias += warp_delta;
+        if (rexec_is_enabled()) {
+            if (next_vm_deadline > 0) {
+                timers_state.qemu_icount_bias += next_vm_deadline;
+            }
+        } else {
+            timers_state.qemu_icount_bias += warp_delta;
+        }
     }
     vm_clock_warp_start = -1;
     seqlock_write_unlock(&timers_state.vm_clock_seqlock);
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 0ae7f28..de2641a 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -754,6 +754,14 @@ int64_t cpu_get_icount(int with_bias);
 int64_t cpu_get_clock(void);
 int64_t cpu_icount_to_ns(int64_t icount);
 
+/**
+ * void icount_warp_rt:
+ *
+ * Move icount to the realtime clock or to the next QEMU_VIRTUAL_CLOCK event
+ * when reverse execution is enabled.
+ */
+void icount_warp_rt(void *opaque);
+
 /*******************************************/
 /* host CPU ticks (if available) */
 
diff --git a/include/reverse-execution.h b/include/reverse-execution.h
index 9951549..871d5ee 100644
--- a/include/reverse-execution.h
+++ b/include/reverse-execution.h
@@ -25,6 +25,8 @@
 #ifndef REVERSE_EXECUTION
 #define REVERSE_EXECUTION
 
+#include "qom/cpu.h"
+
 void rexec_setup(void);
 void rexec_step_backward(CPUState *cpu, uint64_t steps);
 void rexec_stop_stepping_back_mode(void);
diff --git a/main-loop.c b/main-loop.c
index 8a85493..0e4404b 100644
--- a/main-loop.c
+++ b/main-loop.c
@@ -34,6 +34,8 @@
 
 #include "qemu/compatfd.h"
 
+#include "reverse-execution.h"
+
 /* If we have signalfd, we mask out the signals we want to handle and then
  * use signalfd to listen for them.  We rely on whatever the current signal
  * handler is to dispatch the signals when we receive them.
@@ -489,6 +491,14 @@ int main_loop_wait(int nonblocking)
 
     qemu_clock_run_all_timers();
 
+    /*
+     * Sometimes deadlock can appears because there is no pending event on
+     * virtual clock.
+     */
+    if (rexec_is_enabled()) {
+        icount_warp_rt(NULL);
+    }
+
     return ret;
 }
 
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 528e161..2192e45 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -39,3 +39,4 @@ stub-obj-$(CONFIG_WIN32) += fd-register.o
 stub-obj-y += cpus.o
 stub-obj-y += kvm.o
 stub-obj-y += qmp_pc_dimm_device_list.o
+stub-obj-y += reverse-execution-stub.o
diff --git a/stubs/cpu-get-icount.c b/stubs/cpu-get-icount.c
index 1968de7..d35948f 100644
--- a/stubs/cpu-get-icount.c
+++ b/stubs/cpu-get-icount.c
@@ -7,3 +7,11 @@ int64_t cpu_get_icount(int with_bias)
 {
     abort();
 }
+
+void icount_warp_rt(void *opaque)
+{
+    /*
+     * Should not happen, as rexec_is_enabled() always return false.
+     */
+    abort();
+}
diff --git a/stubs/reverse-execution-stub.c b/stubs/reverse-execution-stub.c
new file mode 100644
index 0000000..e417d31
--- /dev/null
+++ b/stubs/reverse-execution-stub.c
@@ -0,0 +1,32 @@
+/*
+ *  reverse-execution-stub.c
+ *
+ *  Copyright (C) 2014 : GreenSocs Ltd
+ *      http://www.greensocs.com/ , email: address@hidden
+ *
+ *  Developed by :
+ *  Frederic Konrad   <address@hidden>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdbool.h>
+
+bool rexec_is_enabled(void);
+
+bool rexec_is_enabled(void)
+{
+    return false;
+}
-- 
1.9.0