[v1] x86/cpuidle: get accurate C0 value with xenpm tool

[Huaitong Han <huaitong.han@intel.com>]

When checking the ACPI funciton of C-status, after 100 seconds sleep,
the sampling value of C0 C-status from the xenpm tool decreases.
Because C0=NOW()-C1-C2-C3-C4, when NOW() value is during idle time,
NOW() value is bigger than last C-status update time, and C0 value
is also bigger than ture value. if margin of the second error cannot
make up for margin of the first error, the value of C0 would decrease.

Signed-off-by: Huaitong Han <huaitong.han@intel.com>

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index e639c99..fd80227 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -499,6 +499,7 @@ void update_idle_stats(struct acpi_processor_power *power,
     if ( sleep_ticks > 0 )
     {
         power->last_residency = tick_to_ns(sleep_ticks) / 1000UL;
+        power->last_cx_update_tick = after;
         cx->time += sleep_ticks;
     }
 
@@ -1171,7 +1172,7 @@ uint32_t pmstat_get_cx_nr(uint32_t cpuid)
 int pmstat_get_cx_stat(uint32_t cpuid, struct pm_cx_stat *stat)
 {
     struct acpi_processor_power *power = processor_powers[cpuid];
-    uint64_t idle_usage = 0, idle_res = 0;
+    uint64_t idle_usage = 0, idle_res = 0, last_cx_update_time = 0;
     uint64_t usage[ACPI_PROCESSOR_MAX_POWER], res[ACPI_PROCESSOR_MAX_POWER];
     unsigned int i, nr, nr_pc = 0, nr_cc = 0;
 
@@ -1214,6 +1215,10 @@ int pmstat_get_cx_stat(uint32_t cpuid, struct pm_cx_stat *stat)
             idle_res += res[i];
         }
 
+        spin_lock_irq(&power->stat_lock);
+        last_cx_update_time = tick_to_ns(power->last_cx_update_tick);
+        spin_unlock_irq(&power->stat_lock);
+
         get_hw_residencies(cpuid, &hw_res);
 
 #define PUT_xC(what, n) do { \
@@ -1243,7 +1248,7 @@ int pmstat_get_cx_stat(uint32_t cpuid, struct pm_cx_stat *stat)
     }
 
     usage[0] = idle_usage;
-    res[0] = NOW() - idle_res;
+    res[0] = last_cx_update_time - idle_res;
 
     if ( copy_to_guest(stat->triggers, usage, nr) ||
          copy_to_guest(stat->residencies, res, nr) )
diff --git a/xen/include/xen/cpuidle.h b/xen/include/xen/cpuidle.h
index b7b9e8c..19e7c7a 100644
--- a/xen/include/xen/cpuidle.h
+++ b/xen/include/xen/cpuidle.h
@@ -66,6 +66,7 @@ struct acpi_processor_power
     struct acpi_processor_cx *last_state;
     struct acpi_processor_cx *safe_state;
     void *gdata; /* governor specific data */
+    u64 last_cx_update_tick;
     u32 last_residency;
     u32 count;
     spinlock_t stat_lock;
-- 
1.9.1