Create a field trial to test if we can detect good QPC implementations.

base/cpu.cc

 // Copyright (c) 2012 The Chromium 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 "base/cpu.h"
 
 #include <string.h>
 
 #include <algorithm>
 
@@ skipping 14 matching lines @@
     stepping_(0),
     ext_model_(0),
     ext_family_(0),
     has_mmx_(false),
     has_sse_(false),
     has_sse2_(false),
     has_sse3_(false),
     has_ssse3_(false),
     has_sse41_(false),
     has_sse42_(false),
+    has_nonstoptsc_(false),
     cpu_vendor_("unknown") {
   Initialize();
 }
 
 #if defined(ARCH_CPU_X86_FAMILY)
 #ifndef _MSC_VER
 
 #if defined(__pic__) && defined(__i386__)
 
 void __cpuid(int cpu_info[4], int info_type) {
@@ skipping 71 matching lines @@
     has_sse3_ = (cpu_info[2] & 0x00000001) != 0;
     has_ssse3_ = (cpu_info[2] & 0x00000200) != 0;
     has_sse41_ = (cpu_info[2] & 0x00080000) != 0;
     has_sse42_ = (cpu_info[2] & 0x00100000) != 0;
     has_avx_ = (cpu_info[2] & 0x10000000) != 0;
   }
 
   // Get the brand string of the cpu.
   __cpuid(cpu_info, 0x80000000);
   const int parameter_end = 0x80000004;
+  int max_parameter = cpu_info[0];
 
   if (cpu_info[0] >= parameter_end) {
     char* cpu_string_ptr = cpu_string;
 
     for (int parameter = 0x80000002; parameter <= parameter_end &&
          cpu_string_ptr < &cpu_string[sizeof(cpu_string)]; parameter++) {
       __cpuid(cpu_info, parameter);
       memcpy(cpu_string_ptr, cpu_info, sizeof(cpu_info));
       cpu_string_ptr += sizeof(cpu_info);
     }
     cpu_brand_.assign(cpu_string, cpu_string_ptr - cpu_string);
   }
+
+  const int parameter_containing_nonstoptsc = 0x80000007;
+  if (max_parameter >= parameter_containing_nonstoptsc) {
+    __cpuid(cpu_info, parameter_containing_nonstoptsc);
+    has_nonstoptsc_ = (cpu_info[3] & (1 << 8)) != 0;

[jar (doing other things), 2013/04/04 00:26:13]

nit: unless there is a great reason to write this so compactly, I'd greatly
prefer something like:

has_non_stop_tsc

Even "tsc" bugs me a bit, but I'm not sure about "time_stamp_counter"

hence:
has_non_stop_time_stamp_counter

I don't mind using a special name when there is some crazy intel defined name to
match (example: sse41), but for places where we're not forced to use a name,
perchance we can push toward our style.

[James Simonsen, 2013/04/04 02:26:51]

Done.

+  }
 #endif
 }
 
 CPU::IntelMicroArchitecture CPU::GetIntelMicroArchitecture() const {
   if (has_avx()) return AVX;
   if (has_sse42()) return SSE42;
   if (has_sse41()) return SSE41;
   if (has_ssse3()) return SSSE3;
   if (has_sse3()) return SSE3;
   if (has_sse2()) return SSE2;
   if (has_sse()) return SSE;
   return PENTIUM;
 }
 
 }  // namespace base