Use 3 wave out buffers for all XP configurations (not just single-processor).

media/audio/audio_util.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.
 
 // Software adjust volume of samples, allows each audio stream its own
 // volume without impacting master volume for chrome and other applications.
 
 // Implemented as templates to allow 8, 16 and 32 bit implementations.
 // 8 bit is unsigned and biased by 128.
 
@@ skipping 10 matching lines @@
 #include "base/shared_memory.h"
 #include "base/time.h"
 #include "media/audio/audio_parameters.h"
 #include "media/audio/audio_util.h"
 
 #if defined(OS_MACOSX)
 #include "media/audio/mac/audio_low_latency_input_mac.h"
 #include "media/audio/mac/audio_low_latency_output_mac.h"
 #elif defined(OS_WIN)
 #include "base/command_line.h"
-#include "base/sys_info.h"
 #include "base/win/windows_version.h"
 #include "media/audio/audio_manager_base.h"
 #include "media/audio/win/audio_low_latency_input_win.h"
 #include "media/audio/win/audio_low_latency_output_win.h"
 #include "media/base/media_switches.h"
 #endif
 
 using base::subtle::Atomic32;
 
 const uint32 kUnknownDataSize = static_cast<uint32>(-1);
@@ skipping 493 matching lines @@
 
 #if defined(OS_WIN)
 
 bool IsWASAPISupported() {
   // Note: that function correctly returns that Windows Server 2003 does not
   // support WASAPI.
   return base::win::GetVersion() >= base::win::VERSION_VISTA;
 }
 
 int NumberOfWaveOutBuffers() {
-  // The entire Windows audio stack was rewritten for Windows Vista, and the
-  // wave out API is simulated on top of new API, so there is noticeable
-  // performance degradation compared to Windows XP. So use 4 buffers for Vista.
-  if (base::win::GetVersion() == base::win::VERSION_VISTA)
-    return 4;
-
-  // Part of regression was apparently fixed in Windows 7, but problems remain
-  // at least with some configurations (compared to XP). So use 3 buffers for
-  // Windows 7 and higher.
-  if (base::win::GetVersion() >= base::win::VERSION_WIN7)
-    return 3;
-
-  // Otherwise (for XP), use 3 buffers on single-core systems and 2 otherwise.
-  return (base::SysInfo::NumberOfProcessors() < 2) ? 3 : 2;
+  // Use 4 buffers for Vista, 3 for everyone else:
+  //  - The entire Windows audio stack was rewritten for Windows Vista and wave
+  //    out performance was degraded compared to XP.
+  //  - The regression was fixed in Windows 7 and most configurations will work
+  //    with 2, but some (e.g., some Sound Blasters) still need 3.
+  //  - Some XP configurations (even multi-processor ones) also need 3.
+  return (base::win::GetVersion() == base::win::VERSION_VISTA) ? 4 : 3;
 }
 
 #endif
 
 }  // namespace media