Use a valid /prefetch argument when launching a process.

content/public/common/content_switches.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 "build/build_config.h"
 #include "content/public/common/content_switches.h"
 
 namespace switches {
 
 // The number of MSAA samples for canvas2D. Requires MSAA support by GPU to
@@ skipping 948 matching lines @@
 #endif
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
 // Disables support for Core Animation plugins. This is triggered when
 // accelerated compositing is disabled. See http://crbug.com/122430.
 const char kDisableCoreAnimationPlugins[] =
     "disable-core-animation-plugins";
 #endif
 
 #if defined(OS_WIN)
+// /prefetch:# arguments to use when launching various process types. It has
+// been observed that when file reads are consistent for 3 process launches with
+// the same /prefetch:# argument, the Windows prefetcher starts issuing reads in
+// batch at process launch. Because reads depend on the process type, the
+// prefetcher wouldn't be able to observe consistent reads if no /prefetch:#
+// arguments were used. Note that the browser process has no /prefetch:#
+// argument; as such all other processes must have one in order to avoid
+// polluting its profile. Note: # must always be in [1, 8]; otherwise it is
+// ignored by the// Windows prefetcher.

[gab, 2016/01/29 19:39:28]

rm "//" mid sentence.

[fdoray, 2016/02/01 13:28:26]

Done.

+const char kPrefetchArgumentRenderer[] = "/prefetch:1";
+const char kPrefetchArgumentGpu[] = "/prefetch:2";
+const char kPrefetchArgumentPpapi[] = "/prefetch:3";
+const char kPrefetchArgumentPpapiBroker[] = "/prefetch:4";
+

[gab, 2016/01/29 19:39:28]

I'd remove this empty line to make it even clearer that the follow-up comments
are about the next IDs.

[fdoray, 2016/02/01 13:28:26]

Done.

+// /prefetch:5 is unused to this date and can be claimed by a new process type.
+// /prefetch:6 and /prefetch:7 are reserved for content embedders and are not to
+// be used by content itself.
+
+// /prefetch:# argument shared by all process types that don't have their own.
+// It is likely that the prefetcher won't work for these process types as it
+// won't be able to observe consistent file reads across launches. However,
+// having a valid prefetch argument for these process types is required to
+// prevent them from interfering with the prefetch profile of the browser
+// process.
+const char kPrefetchArgumentOther[] = "/prefetch:8";
+
 // Device scale factor passed to certain processes like renderers, etc.
 const char kDeviceScaleFactor[]     = "device-scale-factor";
 
 // Disable the Legacy Window which corresponds to the size of the WebContents.
 const char kDisableLegacyIntermediateWindow[] = "disable-legacy-window";
 
 // Disables the Win32K process mitigation policy for renderer processes.
 const char kDisableWin32kRendererLockDown[] =
     "disable-win32k-renderer-lockdown";
 
@@ skipping 17 matching lines @@
 const char kMemoryPressureThresholdsMb[] = "memory-pressure-thresholds-mb";
 
 // Enables the exporting of the tracing events to ETW. This is only supported on
 // Windows Vista and later.
 const char kTraceExportEventsToETW[] = "trace-export-events-to-etw";
 #endif
 
 // Don't dump stuff here, follow the same order as the header.
 
 }  // namespace switches