[Qemu-devel] [RFC PATCH 04/12] icount: introduce icount timer.

[fred.konrad@greensocs.com]

From: KONRAD Frederic <fred.konrad@greensocs.com>

This introduces a new timer based only on instruction counter and without any
compensation.

Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
---
 cpus.c                 | 28 +++++++++++++++++++++++-----
 include/qemu/timer.h   |  8 ++++++++
 qemu-timer.c           |  6 ++++++
 stubs/cpu-get-icount.c |  5 +++++
 4 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/cpus.c b/cpus.c
index bdbc431..ba096a3 100644
--- a/cpus.c
+++ b/cpus.c
@@ -132,7 +132,7 @@ typedef struct TimersState {
 static TimersState timers_state;
 
 /* Return the virtual CPU time, based on the instruction counter.  */
-static int64_t cpu_get_icount_locked(void)
+static int64_t cpu_get_icount_locked(int with_bias)
 {
     int64_t icount;
     CPUState *cpu = current_cpu;
@@ -144,7 +144,12 @@ static int64_t cpu_get_icount_locked(void)
         }
         icount -= (cpu->icount_decr.u16.low + cpu->icount_extra);
     }
-    return timers_state.qemu_icount_bias + (icount << icount_time_shift);
+
+    if (with_bias) {
+        return timers_state.qemu_icount_bias + (icount << icount_time_shift);
+    } else {
+        return icount << icount_time_shift;
+    }
 }
 
 int64_t cpu_get_icount(void)
@@ -154,7 +159,20 @@ int64_t cpu_get_icount(void)
 
     do {
         start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
-        icount = cpu_get_icount_locked();
+        icount = cpu_get_icount_locked(true);
+    } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
+
+    return icount;
+}
+
+int64_t cpu_get_icount_wo_bias(void)
+{
+    int64_t icount;
+    unsigned start;
+
+    do {
+        start = seqlock_read_begin(&timers_state.vm_clock_seqlock);
+        icount = cpu_get_icount_locked(false);
     } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
 
     return icount;
@@ -265,7 +283,7 @@ static void icount_adjust(void)
 
     seqlock_write_lock(&timers_state.vm_clock_seqlock);
     cur_time = cpu_get_clock_locked();
-    cur_icount = cpu_get_icount_locked();
+    cur_icount = cpu_get_icount_locked(true);
 
     delta = cur_icount - cur_time;
     /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  */
@@ -328,7 +346,7 @@ static void icount_warp_rt(void *opaque)
              * far ahead of real time.
              */
             int64_t cur_time = cpu_get_clock_locked();
-            int64_t cur_icount = cpu_get_icount_locked();
+            int64_t cur_icount = cpu_get_icount_locked(true);
             int64_t delta = cur_time - cur_icount;
             warp_delta = MIN(warp_delta, delta);
         }
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 7f9a074..da47194 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -36,12 +36,19 @@
  * is suspended, and it will reflect system time changes the host may
  * undergo (e.g. due to NTP). The host clock has the same precision as
  * the virtual clock.
+ *
+ * @QEMU_CLOCK_ICOUNT: icount clock
+ *
+ * The icount clock is based on instruction counter without any compensation for
+ * speed. It will run only when instruction are executed and make only sense in
+ * icount mode.
  */
 
 typedef enum {
     QEMU_CLOCK_REALTIME = 0,
     QEMU_CLOCK_VIRTUAL = 1,
     QEMU_CLOCK_HOST = 2,
+    QEMU_CLOCK_ICOUNT = 3,
     QEMU_CLOCK_MAX
 } QEMUClockType;
 
@@ -743,6 +750,7 @@ static inline int64_t get_clock(void)
 #endif
 
 /* icount */
+int64_t cpu_get_icount_wo_bias(void);
 int64_t cpu_get_icount(void);
 int64_t cpu_get_clock(void);
 
diff --git a/qemu-timer.c b/qemu-timer.c
index e15ce47..8a36906 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -563,6 +563,12 @@ int64_t qemu_clock_get_ns(QEMUClockType type)
             notifier_list_notify(&clock->reset_notifiers, &now);
         }
         return now;
+    case QEMU_CLOCK_ICOUNT:
+        if (use_icount) {
+            return cpu_get_icount_wo_bias();
+        } else {
+            return -1;
+        }
     }
 }
 
diff --git a/stubs/cpu-get-icount.c b/stubs/cpu-get-icount.c
index d685859..fa242f3 100644
--- a/stubs/cpu-get-icount.c
+++ b/stubs/cpu-get-icount.c
@@ -7,3 +7,8 @@ int64_t cpu_get_icount(void)
 {
     abort();
 }
+
+int64_t cpu_get_icount_wo_bias(void)
+{
+    abort();
+}
-- 
1.8.1.4