[Qemu-devel] [RFC PATCH v8 11/21] replay: recording and replaying clock ticks

[Pavel Dovgalyuk]

Clock ticks are considered as the sources of non-deterministic data for
virtual machine. This patch implements saving the clock values when they
are acquired (virtual, host clock, rdtsc, and some other timers).
When replaying the execution corresponding values are read from log and
transfered to the module, which wants to read the values.
Such a design required the clock polling to be synchronized. Sometimes
it is not true - e.g. when timeouts for timer lists are checked. In this case
we use a cached value of the clock, passing it to the client code.

Signed-off-by: Pavel Dovgalyuk <address@hidden>
---
 cpus.c                   |    3 +-
 include/qemu/timer.h     |   10 +++++
 qemu-timer.c             |    7 ++--
 replay/Makefile.objs     |    1 +
 replay/replay-internal.h |   13 +++++++
 replay/replay-time.c     |   84 ++++++++++++++++++++++++++++++++++++++++++++++
 replay/replay.h          |   25 ++++++++++++++
 stubs/replay.c           |    9 +++++
 8 files changed, 147 insertions(+), 5 deletions(-)
 create mode 100755 replay/replay-time.c

diff --git a/cpus.c b/cpus.c
index 8787277..01d89aa 100644
--- a/cpus.c
+++ b/cpus.c
@@ -353,7 +353,8 @@ static void icount_warp_rt(void *opaque)
 
     seqlock_write_lock(&timers_state.vm_clock_seqlock);
     if (runstate_is_running()) {
-        int64_t clock = cpu_get_clock_locked();
+        int64_t clock = REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT,
+                                     cpu_get_clock_locked());
         int64_t warp_delta;
 
         warp_delta = clock - vm_clock_warp_start;
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 0666920..0c2472c 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -4,6 +4,7 @@
 #include "qemu/typedefs.h"
 #include "qemu-common.h"
 #include "qemu/notify.h"
+#include "replay/replay.h"
 
 /* timers */
 
@@ -760,6 +761,8 @@ int64_t cpu_icount_to_ns(int64_t icount);
 /*******************************************/
 /* host CPU ticks (if available) */
 
+#define cpu_get_real_ticks cpu_get_real_ticks_impl
+
 #if defined(_ARCH_PPC)
 
 static inline int64_t cpu_get_real_ticks(void)
@@ -913,6 +916,13 @@ static inline int64_t cpu_get_real_ticks (void)
 }
 #endif
 
+#undef cpu_get_real_ticks
+
+static inline int64_t cpu_get_real_ticks(void)
+{
+    return REPLAY_CLOCK(REPLAY_CLOCK_REAL_TICKS, cpu_get_real_ticks_impl());
+}
+
 #ifdef CONFIG_PROFILER
 static inline int64_t profile_getclock(void)
 {
diff --git a/qemu-timer.c b/qemu-timer.c
index 98d9d1b..bc981a2 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -25,6 +25,7 @@
 #include "sysemu/sysemu.h"
 #include "monitor/monitor.h"
 #include "ui/console.h"
+#include "replay/replay.h"
 
 #include "hw/hw.h"
 
@@ -566,15 +567,15 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
             return cpu_get_clock();
         }
     case QEMU_CLOCK_HOST:
-        now = get_clock_realtime();
+        now = REPLAY_CLOCK(REPLAY_CLOCK_HOST, get_clock_realtime());
         last = clock->last;
         clock->last = now;
-        if (now < last) {
+        if (now < last && replay_mode == REPLAY_MODE_NONE) {
             notifier_list_notify(&clock->reset_notifiers, &now);
         }
         return now;
     case QEMU_CLOCK_VIRTUAL_RT:
-        return cpu_get_clock();
+        return REPLAY_CLOCK(REPLAY_CLOCK_VIRTUAL_RT, cpu_get_clock());
     }
 }
 
diff --git a/replay/Makefile.objs b/replay/Makefile.objs
index 56da09c..257c320 100755
--- a/replay/Makefile.objs
+++ b/replay/Makefile.objs
@@ -1,3 +1,4 @@
 obj-y += replay.o
 obj-y += replay-internal.o
 obj-y += replay-events.o
+obj-y += replay-time.o
diff --git a/replay/replay-internal.h b/replay/replay-internal.h
index 1666d6e..e906ec3 100755
--- a/replay/replay-internal.h
+++ b/replay/replay-internal.h
@@ -22,7 +22,10 @@ enum ReplayEvents {
     /* for emulated exceptions */
     EVENT_EXCEPTION,
     /* for async events */
-    EVENT_ASYNC
+    EVENT_ASYNC,
+    /* for clock read/writes */
+    /* some of grteater codes are reserved for clocks */
+    EVENT_CLOCK
 };
 
 /* Asynchronous events IDs */
@@ -34,6 +37,8 @@ enum ReplayAsyncEventKind {
 typedef enum ReplayAsyncEventKind ReplayAsyncEventKind;
 
 typedef struct ReplayState {
+    /*! Cached clock values. */
+    int64_t cached_clock[REPLAY_CLOCK_COUNT];
     /*! Current step - number of processed instructions and timer events. */
     uint64_t current_step;
     /*! Number of instructions to be executed before other events happen. */
@@ -88,6 +93,12 @@ bool skip_async_events(int stop_event);
     reports an error and stops the execution. */
 void skip_async_events_until(unsigned int kind);
 
+/*! Reads next clock value from the file.
+    If clock kind read from the file is different from the parameter,
+    the value is not used.
+    If the parameter is -1, the clock value is read to the cache anyway. */
+void replay_read_next_clock(unsigned int kind);
+
 /* Asynchronous events queue */
 
 /*! Initializes events' processing internals */
diff --git a/replay/replay-time.c b/replay/replay-time.c
new file mode 100755
index 0000000..5f5bc6a
--- /dev/null
+++ b/replay/replay-time.c
@@ -0,0 +1,84 @@
+/*
+ * replay-time.c
+ *
+ * Copyright (c) 2010-2015 Institute for System Programming
+ *                         of the Russian Academy of Sciences.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "replay.h"
+#include "replay-internal.h"
+
+
+int64_t replay_save_clock(ReplayClockKind kind, int64_t clock)
+{
+    replay_save_instructions();
+
+    if (kind >= REPLAY_CLOCK_COUNT) {
+        fprintf(stderr, "invalid clock ID %d for replay\n", kind);
+        exit(1);
+    }
+
+    if (replay_file) {
+        replay_mutex_lock();
+        replay_put_event(EVENT_CLOCK + kind);
+        replay_put_qword(clock);
+        replay_mutex_unlock();
+    }
+
+    return clock;
+}
+
+void replay_read_next_clock(ReplayClockKind kind)
+{
+    replay_fetch_data_kind();
+    if (replay_file) {
+        unsigned int read_kind = replay_data_kind - EVENT_CLOCK;
+
+        if (kind != -1 && read_kind != kind) {
+            return;
+        }
+        if (read_kind >= REPLAY_CLOCK_COUNT) {
+            fprintf(stderr,
+                    "invalid clock ID %d was read from replay\n", read_kind);
+            exit(1);
+        }
+
+        int64_t clock = replay_get_qword();
+
+        replay_check_error();
+        replay_has_unread_data = 0;
+
+        replay_state.cached_clock[read_kind] = clock;
+    }
+}
+
+/*! Reads next clock event from the input. */
+int64_t replay_read_clock(ReplayClockKind kind)
+{
+    if (kind >= REPLAY_CLOCK_COUNT) {
+        fprintf(stderr, "invalid clock ID %d for replay\n", kind);
+        exit(1);
+    }
+
+    replay_exec_instructions();
+
+    if (replay_file) {
+        int64_t ret;
+        replay_mutex_lock();
+        if (skip_async_events(EVENT_CLOCK + kind)) {
+            replay_read_next_clock(kind);
+        }
+        ret = replay_state.cached_clock[kind];
+        replay_mutex_unlock();
+
+        return ret;
+    }
+
+    fprintf(stderr, "REPLAY INTERNAL ERROR %d\n", __LINE__);
+    exit(1);
+}
diff --git a/replay/replay.h b/replay/replay.h
index 31ca3b9..8a8e7e0 100755
--- a/replay/replay.h
+++ b/replay/replay.h
@@ -16,6 +16,18 @@
 #include <stdint.h>
 #include "qapi-types.h"
 
+/* replay clock kinds */
+enum ReplayClockKind {
+    /* rdtsc */
+    REPLAY_CLOCK_REAL_TICKS,
+    /* host_clock */
+    REPLAY_CLOCK_HOST,
+    /* virtual_rt_clock */
+    REPLAY_CLOCK_VIRTUAL_RT,
+    REPLAY_CLOCK_COUNT
+};
+typedef enum ReplayClockKind ReplayClockKind;
+
 extern ReplayMode replay_mode;
 
 /* Processing the instructions */
@@ -43,6 +55,19 @@ bool replay_interrupt(void);
     Returns true, when interrupt request is pending */
 bool replay_has_interrupt(void);
 
+/* Processing clocks and other time sources */
+
+/*! Save the specified clock */
+int64_t replay_save_clock(ReplayClockKind kind, int64_t clock);
+/*! Read the specified clock from the log or return cached data */
+int64_t replay_read_clock(ReplayClockKind kind);
+/*! Saves or reads the clock depending on the current replay mode. */
+#define REPLAY_CLOCK(clock, value)                                      \
+    (replay_mode == REPLAY_MODE_PLAY ? replay_read_clock((clock))       \
+        : replay_mode == REPLAY_MODE_RECORD                             \
+            ? replay_save_clock((clock), (value))                       \
+        : (value))
+
 /* Asynchronous events queue */
 
 /*! Disables storing events in the queue */
diff --git a/stubs/replay.c b/stubs/replay.c
index 563c777..121bca6 100755
--- a/stubs/replay.c
+++ b/stubs/replay.c
@@ -1,3 +1,12 @@
 #include "replay/replay.h"
 
 ReplayMode replay_mode;
+
+int64_t replay_save_clock(unsigned int kind, int64_t clock)
+{
+}
+
+int64_t replay_read_clock(unsigned int kind)
+{
+    return 0;
+}