cputime optimize for arm64

src/butil/time.cpp

@@ -143,16 +143,22 @@ int64_t read_cpu_frequency(bool* invariant_tsc) {
 }
 
 // Return value must be >= 0
-int64_t read_invariant_cpu_frequency() {
+static int64_t read_invariant_cpu_frequency() {
     bool invariant_tsc = false;
-    const int64_t freq = read_cpu_frequency(&invariant_tsc);
+    int64_t freq = -1;
+#if defined(__aarch64__)
+    __asm__ __volatile__("mrs %0, CNTFRQ_EL0" : "=r"(freq));
+#else
+    freq = read_cpu_frequency(&invariant_tsc);
     if (!invariant_tsc || freq < 0) {
         return 0;
     }
+#endif
+
     return freq;
 }
 
-int64_t invariant_cpu_freq = -1;
+int64_t invariant_cpu_freq = read_invariant_cpu_frequency();
 }  // namespace detail
 
 }  // namespace butil

src/butil/time.h

@@ -265,7 +265,7 @@ inline uint64_t clock_cycles() {
   #error "unsupported arch"
 #endif
 }
-extern int64_t read_invariant_cpu_frequency();
+
 // Be positive iff:
 // 1 Intel x86_64 CPU (multiple cores) supporting constant_tsc and
 // nonstop_tsc(check flags in /proc/cpuinfo)
@@ -279,7 +279,7 @@ extern int64_t invariant_cpu_freq;
 // note: Inlining shortens time cost per-call for 15ns in a loop of many
 //       calls to this function.
 inline int64_t cpuwide_time_ns() {
-#if !defined(BAIDU_INTERNAL)
+#if !defined(BAIDU_INTERNAL) && !defined(__aarch64__)
     // nearly impossible to get the correct invariant cpu frequency on
     // different CPU and machines. CPU-ID rarely works and frequencies
     // in "model name" and "cpu Mhz" are both unreliable.
@@ -298,14 +298,9 @@ inline int64_t cpuwide_time_ns() {
         const uint64_t remain = tsc % cpu_freq;
         // TODO: should be OK until CPU's frequency exceeds 16GHz.
         return remain * 1000000000L / cpu_freq + sec * 1000000000L;
-    } else if (!cpu_freq) {
+    } else {
         // Lack of necessary features, return system-wide monotonic time instead.
         return monotonic_time_ns();
-    } else {
-        // Use a thread-unsafe method(OK to us) to initialize the freq
-        // to save a "if" test comparing to using a local static variable
-        detail::invariant_cpu_freq = detail::read_invariant_cpu_frequency();
-        return cpuwide_time_ns();
     }
 #endif // defined(BAIDU_INTERNAL)
 }