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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/app_launch_prefetch/app_launch_prefetch.h"
#include <tuple>
#include "base/command_line.h"
#include "base/feature_list.h"
#include "base/notreached.h"
#include "base/win/windows_version.h"
namespace app_launch_prefetch {
namespace {
BASE_FEATURE(kExpandedPrefetchRange,
"ExpandedPrefetchRange",
base::FEATURE_ENABLED_BY_DEFAULT);
// /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.
// On Windows versions before Win11 21H2 the value must always be in [1, 8];
// otherwise it is treated as 0 by the Windows prefetcher and will interfere
// with the main process launch.
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument1 = {L"/prefetch:1", 1};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument2 = {L"/prefetch:2", 2};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument3 = {L"/prefetch:3", 3};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument4 = {L"/prefetch:4", 4};
// /prefetch:5, /prefetch:6 and /prefetch:7 are reserved for content embedders
// and are not to be used by content itself, with caveats: we violate this
// rule with kBrowserBackground using bucket 5, while the 7th bucket is used by
// the crashpad fallback handler.
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument5 = {L"/prefetch:5", 5};
// constexpr base::CommandLine::StringViewType kPrefetchArgument6 =
// "/prefetch:6";
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument7 = {L"/prefetch:7", 7};
// Catch all for Windows versions before Win 11 21H2.
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument8 = {L"/prefetch:8", 8};
// On Windows 11 21H2 and later the prefetch range was expanded to be [1,16]
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument9 = {L"/prefetch:9", 9};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument10 = {L"/prefetch:10", 10};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument11 = {L"/prefetch:11", 11};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument12 = {L"/prefetch:12", 12};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument13 = {L"/prefetch:13", 13};
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument14 = {L"/prefetch:14", 14};
// constexpr base::CommandLine::StringViewType kPrefetchArgument15 =
// "/prefetch:15";
// Catch all for Windows versions Win 11 21H2 and later.
constexpr std::tuple<base::CommandLine::StringViewType, int>
kPrefetchArgument16 = {L"/prefetch:16", 16};
const std::tuple<base::CommandLine::StringViewType, int>& GetPrefetchInfo(
SubprocessType type) {
using enum SubprocessType;
if (base::win::GetVersion() >= base::win::Version::WIN11 &&
base::FeatureList::GetInstance() &&
base::FeatureList::IsEnabled(kExpandedPrefetchRange)) {
// These are the prefetch arguments used on Windows versions
// for Win11 and later. There are fewer processes using the same
// values and this should lead to better App Launch PreFetch (ALPF)
// behavior.
// kPrefetchArgument8 and kPrefetchArgument15 are currently unused.
switch (type) {
case kBrowser:
NOTREACHED();
case kRenderer:
return kPrefetchArgument1;
case kGPU:
return kPrefetchArgument2;
case kPpapi:
return kPrefetchArgument3;
case kCrashpad:
return kPrefetchArgument4;
case kBrowserBackground:
return kPrefetchArgument5;
case kCrashpadFallback:
return kPrefetchArgument7;
case kExtension:
return kPrefetchArgument9;
case kGPUInfo:
return kPrefetchArgument10;
case kUtilityNetworkService:
return kPrefetchArgument11;
case kUtilityAudio:
return kPrefetchArgument12;
case kUtilityStorage:
return kPrefetchArgument13;
case kUtilityOther:
return kPrefetchArgument14;
case kCatchAll:
return kPrefetchArgument16;
}
} else {
// These are the prefetch arguments used on Windows versions
// before Win11 21H2. There are multiple processes using the same values
// and this leads to less than optimal App Launch PreFetch (ALPF) behavior.
// /prefetch:5, /prefetch:6 and /prefetch:7 are reserved for content
// embedders and are not to be used by content itself, with caveats: we
// violate this rule with kBrowserBackground using bucket 5, while the 7th
// bucket is used by the crashpad fallback handler.
switch (type) {
case kBrowser:
NOTREACHED();
case kRenderer:
return kPrefetchArgument1;
case kGPU:
return kPrefetchArgument2;
case kExtension:
return kPrefetchArgument2;
case kPpapi:
return kPrefetchArgument3;
case kUtilityNetworkService:
return kPrefetchArgument3;
case kCrashpad:
return kPrefetchArgument4;
case kBrowserBackground:
return kPrefetchArgument5;
case kCrashpadFallback:
return kPrefetchArgument7;
case kGPUInfo:
return kPrefetchArgument8;
case kUtilityAudio:
return kPrefetchArgument8;
case kUtilityStorage:
return kPrefetchArgument8;
case kUtilityOther:
return kPrefetchArgument8;
case kCatchAll:
return kPrefetchArgument8;
}
}
}
} // namespace
base::CommandLine::StringViewType GetPrefetchSwitch(SubprocessType type) {
return std::get<0>(GetPrefetchInfo(type));
}
uint32_t GetPrefetchBucket(SubprocessType type) {
return std::get<1>(GetPrefetchInfo(type));
}
} // namespace app_launch_prefetch
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