Revert of Use CLOCK_REALTIME_COARSE when available.

src/base/platform/time.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/platform/time.h"
 
 #if V8_OS_POSIX
 #include <fcntl.h>  // for O_RDONLY
 #include <sys/time.h>
 #include <unistd.h>
 #endif
 #if V8_OS_MACOSX
 #include <mach/mach_time.h>
 #endif
 
 #include <cstring>
 #include <ostream>
 
 #if V8_OS_WIN
 #include "src/base/lazy-instance.h"
 #include "src/base/win32-headers.h"
 #endif
 #include "src/base/cpu.h"
 #include "src/base/logging.h"
 #include "src/base/platform/platform.h"
 
-// CLOCK_REALTIME_COARSE was added in Linux 2.6.32.
-#if V8_OS_LINUX && !defined(CLOCK_REALTIME_COARSE)
-#define CLOCK_REALTIME_COARSE 5
-#endif
-
 namespace v8 {
 namespace base {
 
 TimeDelta TimeDelta::FromDays(int days) {
   return TimeDelta(days * Time::kMicrosecondsPerDay);
 }
 
 
 TimeDelta TimeDelta::FromHours(int hours) {
   return TimeDelta(hours * Time::kMicrosecondsPerHour);
@@ skipping 208 matching lines @@
   }
   uint64_t us = static_cast<uint64_t>(us_ + kTimeToEpochInMicroseconds) * 10;
   ft.dwLowDateTime = static_cast<DWORD>(us);
   ft.dwHighDateTime = static_cast<DWORD>(us >> 32);
   return ft;
 }
 
 #elif V8_OS_POSIX
 
 Time Time::Now() {
-#ifdef CLOCK_REALTIME_COARSE
-  struct timespec ts;
-  // clockid_t is an int32_t; loads and stores are atomic.
-  static const clockid_t kInvalidClockId = static_cast<clockid_t>(-1);
-  static clockid_t clock_id = kInvalidClockId;
-  if (V8_UNLIKELY(clock_id == kInvalidClockId)) {
-    // CLOCK_REALTIME_COARSE is not supported on Linux kernels < 2.6.32.
-    // Probe the kernel to see if it's available and has <= 1 ms resolution.
-    //
-    // CLOCK_REALTIME_COARSE, unlike CLOCK_REALTIME, can often be serviced
-    // entirely from the vDSO without the need to make a system call.
-    // It can have a dramatic impact on applications that frequently
-    // query the current time.
-    //
-    // One caveat is that CLOCK_REALTIME_COARSE is tied to CONFIG_HZ, the
-    // number of ticks per second that the kernel runs at.  Its granularity
-    // can be as low as one update every 300 ms so we need to make sure that
-    // it is accurate enough.  Fortunately, many if not most kernels are built
-    // with CONFIG_HZ=1000, giving it a one millisecond precision and that is
-    // good enough for our purposes.
-    if (clock_getres(CLOCK_REALTIME_COARSE, &ts) < 0 || ts.tv_sec > 0 ||
-        ts.tv_nsec > 1000 * 1000) {
-      clock_id = CLOCK_REALTIME;  // Not available or not suitable.
-    } else {
-      clock_id = CLOCK_REALTIME_COARSE;
-    }
-  }
-  int result = clock_gettime(clock_id, &ts);
-  DCHECK_EQ(0, result);
-  USE(result);
-  return FromTimespec(ts);
-#else
   struct timeval tv;
   int result = gettimeofday(&tv, NULL);
   DCHECK_EQ(0, result);
   USE(result);
   return FromTimeval(tv);
-#endif
 }
 
 
 Time Time::NowFromSystemTime() {
   return Now();
 }
 
 
 Time Time::FromTimespec(struct timespec ts) {
   DCHECK(ts.tv_nsec >= 0);
@@ skipping 368 matching lines @@
 
 
 // static
 bool TimeTicks::KernelTimestampAvailable() {
   return kernel_tick_clock.Pointer()->Available();
 }
 
 #endif  // V8_OS_WIN
 
 } }  // namespace v8::base