X-Git-Url: http://v3vee.org/palacios/gitweb/gitweb.cgi?a=blobdiff_plain;f=palacios%2Fsrc%2Fpalacios%2Fvmm_time.c;h=27bb2fc97c00b7feeb1785bfcd58f6b6d75f1e10;hb=0e26b3738daf436ba2d9a088ba620a3583d40de3;hp=fc2e37e812a019428717ef1929b4be6e0480b93f;hpb=a8627ddaccf49073eb04286c5ea4767e2903c351;p=palacios.git

diff --git a/palacios/src/palacios/vmm_time.c b/palacios/src/palacios/vmm_time.c
index fc2e37e..27bb2fc 100644
--- a/palacios/src/palacios/vmm_time.c
+++ b/palacios/src/palacios/vmm_time.c
@@ -104,66 +104,109 @@ int v3_offset_time( struct guest_info * info, sint64_t offset )
     return 0;
 }
 
-// Control guest time in relation to host time so that the two stay 
-// appropriately synchronized to the extent possible. 
-int v3_adjust_time(struct guest_info * info) {
+#ifdef V3_CONFIG_TIME_DILATION
+static uint64_t compute_target_host_time(struct guest_info * info, uint64_t guest_time)
+{
     struct vm_time * time_state = &(info->time_state);
-    uint64_t host_time, target_host_time;
-    uint64_t guest_time, target_guest_time, old_guest_time;
-    uint64_t guest_elapsed, host_elapsed, desired_elapsed;
-
-    /* Compute the target host time given how much time has *already*
-     * passed in the guest */
-    guest_time = v3_get_guest_time(time_state);
+    uint64_t guest_elapsed, desired_elapsed;
+    
     guest_elapsed = (guest_time - time_state->initial_time);
     desired_elapsed = (guest_elapsed * time_state->host_cpu_freq) / time_state->guest_cpu_freq;
-    target_host_time = time_state->initial_time + desired_elapsed;
+    return time_state->initial_time + desired_elapsed;
+}
+
+static uint64_t compute_target_guest_time(struct guest_info *info)
+{
+    struct vm_time * time_state = &(info->time_state);
+    uint64_t host_elapsed, desired_elapsed;
+
+    host_elapsed = v3_get_host_time(time_state) - time_state->initial_time;
+    desired_elapsed = (host_elapsed * time_state->guest_cpu_freq) / time_state->host_cpu_freq;
+
+    return time_state->initial_time + desired_elapsed;
+
+} 
+
+/* Yield time in the host to deal with a guest that wants to run slower than 
+ * the native host cycle frequency */
+static int yield_host_time(struct guest_info * info) {
+    struct vm_time * time_state = &(info->time_state);
+    uint64_t host_time, target_host_time;
+    uint64_t guest_time, old_guest_time;
 
     /* Now, let the host run while the guest is stopped to make the two
-     * sync up. */
+     * sync up. Note that this doesn't assume that guest time is stopped;
+     * the offsetting in the next step will change add an offset to guest
+     * time to account for the time paused even if the geust isn't 
+     * usually paused in the VMM. */
     host_time = v3_get_host_time(time_state);
-    old_guest_time = v3_get_guest_time(time_state);
+    old_guest_time = v3_compute_guest_time(time_state, host_time);
+    target_host_time = compute_target_host_time(info, old_guest_time);
 
     while (target_host_time > host_time) {
 	v3_yield(info);
 	host_time = v3_get_host_time(time_state);
     }
 
-    guest_time = v3_get_guest_time(time_state);
+    guest_time = v3_compute_guest_time(time_state, host_time);
 
-    // We do *not* assume the guest timer was paused in the VM. If it was
-    // this offseting is 0. If it wasn't we need this.
+    /* We do *not* assume the guest timer was paused in the VM. If it was
+     * this offseting is 0. If it wasn't, we need this. */
     v3_offset_time(info, (sint64_t)old_guest_time - (sint64_t)guest_time);
 
+    return 0;
+}
+
+static int skew_guest_time(struct guest_info * info) {
+    struct vm_time * time_state = &(info->time_state);
+    uint64_t target_guest_time, guest_time;
     /* Now the host may have gotten ahead of the guest because
      * yielding is a coarse grained thing. Figure out what guest time
      * we want to be at, and use the use the offsetting mechanism in 
      * the VMM to make the guest run forward. We limit *how* much we skew 
      * it forward to prevent the guest time making large jumps, 
      * however. */
-    host_elapsed = host_time - time_state->initial_time;
-    desired_elapsed = (host_elapsed * time_state->guest_cpu_freq) / time_state->host_cpu_freq;
-    target_guest_time = time_state->initial_time + desired_elapsed;
+    target_guest_time = compute_target_guest_time(info);
+    guest_time = v3_get_guest_time(time_state);
 
     if (guest_time < target_guest_time) {
-	uint64_t max_skew, desired_skew, skew;
+	sint64_t max_skew, desired_skew, skew;
 
 	if (time_state->enter_time) {
-	    max_skew = (time_state->exit_time - time_state->enter_time) / 10;
+	    /* Limit forward skew to 10% of the amount the guest has
+	     * run since we last could skew time */
+	    max_skew = ((sint64_t)guest_time - (sint64_t)time_state->enter_time) / 10;
 	} else {
 	    max_skew = 0;
 	}
 
-	desired_skew = target_guest_time - guest_time;
+	desired_skew = (sint64_t)target_guest_time - (sint64_t)guest_time;
 	skew = desired_skew > max_skew ? max_skew : desired_skew;
-/*	PrintDebug("Guest %llu cycles behind where it should be.\n",
+	PrintDebug("Guest %lld cycles behind where it should be.\n",
 		   desired_skew);
-	PrintDebug("Limit on forward skew is %llu. Skewing forward %llu.\n",
-	           max_skew, skew); */
+	PrintDebug("Limit on forward skew is %lld. Skewing forward %lld.\n",
+	           max_skew, skew); 
 	
 	v3_offset_time(info, skew);
     }
-    
+
+    return 0;
+}
+#endif /* V3_CONFIG_TIME_DILATION */
+
+// Control guest time in relation to host time so that the two stay 
+// appropriately synchronized to the extent possible. 
+int v3_adjust_time(struct guest_info * info) {
+
+#ifdef V3_CONFIG_TIME_DILATION
+    /* First deal with yielding if we want to slow down the guest */
+    yield_host_time(info);
+
+    /* Now, if the guest is too slow, (either from excess yielding above,
+     * or because the VMM is doing something that takes a long time to emulate)
+     * allow guest time to jump forward a bit */
+    skew_guest_time(info);
+#endif
     return 0;
 }
 
@@ -185,15 +228,14 @@ v3_time_enter_vm( struct guest_info * info )
     struct vm_time * time_state = &(info->time_state);
     uint64_t guest_time, host_time;
 
-    guest_time = v3_get_guest_time(time_state);
     host_time = v3_get_host_time(time_state);
+    guest_time = v3_get_guest_time(time_state);
     time_state->enter_time = host_time;
-    time_state->guest_host_offset = guest_time - host_time;
-
-    // Because we just modified the offset - shouldn't matter as this should be 
-    // the last time-related call prior to entering the VMM, but worth it 
-    // just in case.
-    time_state->exit_time = host_time; 
+#ifdef V3_CONFIG_TIME_DILATION
+    time_state->guest_host_offset = (sint64_t)guest_time - (sint64_t)host_time;
+#else
+    time_state->guest_host_offset = 0;
+#endif
 
     return 0;
 }
@@ -232,7 +274,9 @@ void v3_update_timers(struct guest_info * info) {
 
     time_state->last_update = v3_get_guest_time(time_state);
     cycles = time_state->last_update - old_time;
+    V3_ASSERT(cycles >= 0);
 
+    //    V3_Print("Updating timers with %lld elapsed cycles.\n", cycles);
     list_for_each_entry(tmp_timer, &(time_state->timers), timer_link) {
 	tmp_timer->ops->update_timer(info, cycles, time_state->guest_cpu_freq, tmp_timer->private_data);
     }