Update CPU idle tracking for apple hosts

The previous setup did not properly consider hyperthreads (at least in local
testing), which likely skews CI results as well. The new code is both simpler
and hopefully will produce more accurate results.

src/ci/cpu-usage-over-time.py

@@ -108,37 +108,37 @@ def idle_since(self, prev):
     from ctypes import *
     libc = cdll.LoadLibrary('/usr/lib/libc.dylib')
 
-    PROESSOR_CPU_LOAD_INFO = c_int(2)
+    class host_cpu_load_info_data_t(Structure):
+        _fields_ = [("cpu_ticks", c_uint * 4)]
+
+    host_statistics = libc.host_statistics
+    host_statistics.argtypes = [
+        c_uint,
+        c_int,
+        POINTER(host_cpu_load_info_data_t),
+        POINTER(c_int)
+    ]
+    host_statistics.restype = c_int
+
     CPU_STATE_USER = 0
     CPU_STATE_SYSTEM = 1
     CPU_STATE_IDLE = 2
     CPU_STATE_NICE = 3
-    c_int_p = POINTER(c_int)
-
     class State:
         def __init__(self):
-            num_cpus_u = c_uint(0)
-            cpu_info = c_int_p()
-            cpu_info_cnt = c_int(0)
-            err = libc.host_processor_info(
+            stats = host_cpu_load_info_data_t()
+            count = c_int(4) # HOST_CPU_LOAD_INFO_COUNT
+            err = libc.host_statistics(
                 libc.mach_host_self(),
-                PROESSOR_CPU_LOAD_INFO,
-                byref(num_cpus_u),
-                byref(cpu_info),
-                byref(cpu_info_cnt),
+                c_int(3), # HOST_CPU_LOAD_INFO
+                byref(stats),
+                byref(count),
             )
             assert err == 0
-            self.user = 0
-            self.system = 0
-            self.idle = 0
-            self.nice = 0
-            cur = 0
-            while cur < cpu_info_cnt.value:
-                self.user += cpu_info[cur + CPU_STATE_USER]
-                self.system += cpu_info[cur + CPU_STATE_SYSTEM]
-                self.idle += cpu_info[cur + CPU_STATE_IDLE]
-                self.nice += cpu_info[cur + CPU_STATE_NICE]
-                cur += num_cpus_u.value
+            self.system = stats.cpu_ticks[CPU_STATE_SYSTEM]
+            self.user = stats.cpu_ticks[CPU_STATE_USER]
+            self.idle = stats.cpu_ticks[CPU_STATE_IDLE]
+            self.nice = stats.cpu_ticks[CPU_STATE_NICE]
 
         def idle_since(self, prev):
             user = self.user - prev.user