[Qemu-devel] [RFC 13/14] Enable negative icount values for QEMU.

[Christopher Covington]

The icount setting specifies how far to shift the instruction
count as a ratio of ns to tie system time to instruction count.
Allow a negative value (i.e. a right shift instead of a left shift)
to be used.

Written by Pat Galizia.

Signed-off-by: Christopher Covington <address@hidden>
---
 cpus.c              | 17 +++++++++++++----
 target-arm/helper.c | 14 ++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/cpus.c b/cpus.c
index 62d157a..1c92a85 100644
--- a/cpus.c
+++ b/cpus.c
@@ -110,6 +110,8 @@ static int64_t vm_clock_warp_start = -1;
 static int icount_time_shift;
 /* Arbitrarily pick 1MIPS as the minimum allowable speed.  */
 #define MAX_ICOUNT_SHIFT 10
+/* In cases where we have a negative icount shift, specify a lower bound. */
+#define MIN_ICOUNT_SHIFT -5
 
 static QEMUTimer *icount_rt_timer;
 static QEMUTimer *icount_vm_timer;
@@ -174,6 +176,8 @@ int64_t cpu_get_icount(void)
 
 int64_t cpu_icount_to_ns(int64_t icount)
 {
+    if (icount_time_shift < 0)
+        return icount >> (-icount_time_shift);
     return icount << icount_time_shift;
 }
 
@@ -271,6 +275,7 @@ static void icount_adjust(void)
     int64_t cur_time;
     int64_t cur_icount;
     int64_t delta;
+    int64_t icount_shifted;
 
     /* Protected by TimersState mutex.  */
     static int64_t last_delta;
@@ -287,8 +292,8 @@ static void icount_adjust(void)
     delta = cur_icount - cur_time;
     /* FIXME: This is a very crude algorithm, somewhat prone to oscillation.  
*/
     if (delta > 0
-        && last_delta + ICOUNT_WOBBLE < delta * 2
-        && icount_time_shift > 0) {
+            && last_delta + ICOUNT_WOBBLE < delta * 2
+            && icount_time_shift > MIN_ICOUNT_SHIFT) {
         /* The guest is getting too far ahead.  Slow time down.  */
         icount_time_shift--;
     }
@@ -299,8 +304,10 @@ static void icount_adjust(void)
         icount_time_shift++;
     }
     last_delta = delta;
-    timers_state.qemu_icount_bias = cur_icount
-                              - (timers_state.qemu_icount << 
icount_time_shift);
+    icount_shifted = (icount_time_shift >= 0) ?
+            timers_state.qemu_icount << icount_time_shift :
+            timers_state.qemu_icount >> (-icount_time_shift);
+    timers_state.qemu_icount_bias = cur_icount - icount_shifted;
     seqlock_write_unlock(&timers_state.vm_clock_seqlock);
 }
 
@@ -321,6 +328,8 @@ static void icount_adjust_vm(void *opaque)
 
 static int64_t qemu_icount_round(int64_t count)
 {
+    if (icount_time_shift < 0)
+        return count;
     return (count + (1 << icount_time_shift) - 1) >> icount_time_shift;
 }
 
diff --git a/target-arm/helper.c b/target-arm/helper.c
index ae0a4ac..0436df5 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -4345,6 +4345,11 @@ void context_check_pid(CPUARMState *env)
 
 void update_instruction_count(CPUARMState *env)
 {
+    CPUState *cpu = CPU(arm_env_get_cpu(env));
+    int prevIoState = cpu->can_do_io;
+    if (use_icount)
+        cpu->can_do_io = 1;
+
     if (bbtrace_initialized()) {
         /*
          * If the bbv plugin is compiled in and enabled, we must account for 
the
@@ -4368,15 +4373,24 @@ void update_instruction_count(CPUARMState *env)
         pmevcntr_increment(env, PMU_COUNTER_TYPE_CYCLES, env->prof_ic);
         env->prof_ic = 0;
     }
+
+    if (use_icount)
+        cpu->can_do_io = prevIoState;
 }
 
 #else //!CONFIG_BBVEC
 
 void update_instruction_count(CPUARMState *env)
 {
+    CPUState *cpu = CPU(arm_env_get_cpu(env));
+    int prevIoState = cpu->can_do_io;
+    if (use_icount)
+        cpu->can_do_io = 1;
     pmevcntr_increment(env, PMU_COUNTER_TYPE_INSTRUCTIONS, env->prof_ic);
     pmevcntr_increment(env, PMU_COUNTER_TYPE_CYCLES, env->prof_ic);
     env->prof_ic = 0;
+    if (use_icount)
+        cpu->can_do_io = prevIoState;
 }
 
 #endif //CONFIG_BBVEC
-- 
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