replay: recording and replaying clock ticks

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).
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 <pavel.dovgaluk@ispras.ru>
Message-Id: <20150917162427.8676.36558.stgit@PASHA-ISP.def.inno>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

cpus.c

@@ -346,7 +346,8 @@ 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;

include/sysemu/replay.h

@@ -16,6 +16,16 @@
 #include <stdint.h>
 #include "qapi-types.h"
 
+/* replay clock kinds */
+enum ReplayClockKind {
+    /* 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 +53,19 @@ 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 */

qemu-timer.c

@@ -24,6 +24,7 @@
 
 #include "qemu/main-loop.h"
 #include "qemu/timer.h"
+#include "sysemu/replay.h"
 
 #ifdef CONFIG_POSIX
 #include <pthread.h>
@@ -570,15 +571,16 @@ 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 || now > (last + get_max_clock_jump())) {
+        if ((now < last || now > (last + get_max_clock_jump()))
+            && 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());
     }
 }
 

replay/Makefile.objs

@@ -1,3 +1,4 @@
 common-obj-y += replay.o
 common-obj-y += replay-internal.o
 common-obj-y += replay-events.o
+common-obj-y += replay-time.o

replay/replay-internal.h

@@ -23,6 +23,10 @@ enum ReplayEvents {
     EVENT_EXCEPTION,
     /* for async events */
     EVENT_ASYNC,
+    /* for clock read/writes */
+    /* some of greater codes are reserved for clocks */
+    EVENT_CLOCK,
+    EVENT_CLOCK_LAST = EVENT_CLOCK + REPLAY_CLOCK_COUNT - 1,
     EVENT_COUNT
 };
 
@@ -35,6 +39,8 @@ 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. */
@@ -85,6 +91,11 @@ void replay_save_instructions(void);
     \return true, if event was found */
 bool replay_next_event_is(int event);
 
+/*! Reads next clock value from the file.
+    If clock kind read from the file is different from the parameter,
+    the value is not used. */
+void replay_read_next_clock(unsigned int kind);
+
 /* Asynchronous events queue */
 
 /*! Initializes events' processing internals */

replay/replay-time.c

@@ -0,0 +1,64 @@
+/*
+ * 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 "sysemu/replay.h"
+#include "replay-internal.h"
+#include "qemu/error-report.h"
+
+int64_t replay_save_clock(ReplayClockKind kind, int64_t clock)
+{
+    replay_save_instructions();
+
+    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)
+{
+    unsigned int read_kind = replay_data_kind - EVENT_CLOCK;
+
+    assert(read_kind == kind);
+
+    int64_t clock = replay_get_qword();
+
+    replay_check_error();
+    replay_finish_event();
+
+    replay_state.cached_clock[read_kind] = clock;
+}
+
+/*! Reads next clock event from the input. */
+int64_t replay_read_clock(ReplayClockKind kind)
+{
+    replay_account_executed_instructions();
+
+    if (replay_file) {
+        int64_t ret;
+        replay_mutex_lock();
+        if (replay_next_event_is(EVENT_CLOCK + kind)) {
+            replay_read_next_clock(kind);
+        }
+        ret = replay_state.cached_clock[kind];
+        replay_mutex_unlock();
+
+        return ret;
+    }
+
+    error_report("REPLAY INTERNAL ERROR %d", __LINE__);
+    exit(1);
+}

stubs/replay.c

@@ -1,3 +1,16 @@
 #include "sysemu/replay.h"
+#include <stdlib.h>
 
 ReplayMode replay_mode;
+
+int64_t replay_save_clock(unsigned int kind, int64_t clock)
+{
+    abort();
+    return 0;
+}
+
+int64_t replay_read_clock(unsigned int kind)
+{
+    abort();
+    return 0;
+}