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jank_injector.cc
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jank_injector.cc
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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "cc/metrics/jank_injector.h"
#include <map>
#include <string>
#include <utility>
#include <vector>
#include "base/debug/alias.h"
#include "base/feature_list.h"
#include "base/functional/bind.h"
#include "base/metrics/field_trial_params.h"
#include "base/no_destructor.h"
#include "base/ranges/algorithm.h"
#include "base/strings/string_split.h"
#include "base/task/single_thread_task_runner.h"
#include "base/time/time.h"
#include "base/trace_event/trace_event.h"
#include "cc/base/features.h"
#include "url/gurl.h"
namespace cc {
namespace {
constexpr char kTraceCategory[] =
"cc,benchmark," TRACE_DISABLED_BY_DEFAULT("devtools.timeline.frame");
const char kJankInjectionAllowedURLs[] = "allowed_urls";
const char kJankInjectionClusterSize[] = "cluster";
const char kJankInjectionTargetPercent[] = "percent";
struct JankInjectionParams {
JankInjectionParams() = default;
~JankInjectionParams() = default;
JankInjectionParams(JankInjectionParams&&) = default;
JankInjectionParams& operator=(JankInjectionParams&&) = default;
JankInjectionParams(const JankInjectionParams&) = delete;
JankInjectionParams& operator=(const JankInjectionParams&) = delete;
// The jank injection code blocks the main thread for |jank_duration| amount
// of time.
base::TimeDelta jank_duration;
// When |busy_loop| is set, blocks the main thread in a busy loop for
// |jank_duration|. Otherwise, sleeps for |jank_duration|.
bool busy_loop = true;
};
bool g_jank_enabled_for_test = false;
bool IsJankInjectionEnabled() {
static bool enabled =
base::FeatureList::IsEnabled(features::kJankInjectionAblationFeature);
return enabled || g_jank_enabled_for_test;
}
using AllowedURLsMap = std::map<std::string, std::vector<std::string>>;
// Returns a map of <host, <list of paths>> pairs.
AllowedURLsMap GetAllowedURLs() {
DCHECK(IsJankInjectionEnabled());
AllowedURLsMap urls;
std::string url_list = base::GetFieldTrialParamValueByFeature(
features::kJankInjectionAblationFeature, kJankInjectionAllowedURLs);
for (auto& it : base::SplitString(url_list, ",", base::TRIM_WHITESPACE,
base::SPLIT_WANT_ALL)) {
GURL url = GURL(it);
urls[url.host()].emplace_back(url.path());
}
return urls;
}
bool IsJankInjectionEnabledForURL(const GURL& url) {
DCHECK(IsJankInjectionEnabled());
static base::NoDestructor<AllowedURLsMap> allowed_urls(GetAllowedURLs());
if (allowed_urls->empty())
return false;
const auto iter = allowed_urls->find(url.host());
if (iter == allowed_urls->end())
return false;
const auto& paths = iter->second;
const auto& path = url.path_piece();
return base::ranges::any_of(paths, [path](const std::string& p) {
return base::StartsWith(path, p);
});
}
void RunJank(JankInjectionParams params) {
TRACE_EVENT0(kTraceCategory, "Injected Jank");
if (params.busy_loop) {
// Do some useless work, and prevent any weird compiler optimization from
// doing anything here.
base::TimeTicks start = base::TimeTicks::Now();
std::vector<base::TimeTicks> dummy;
while (base::TimeTicks::Now() - start < params.jank_duration) {
dummy.push_back(base::TimeTicks::Now());
if (dummy.size() > 100) {
dummy.erase(dummy.begin());
}
}
base::debug::Alias(&dummy);
} else {
base::PlatformThread::Sleep(params.jank_duration);
}
}
} // namespace
ScopedJankInjectionEnabler::ScopedJankInjectionEnabler() {
DCHECK(!g_jank_enabled_for_test);
g_jank_enabled_for_test = true;
}
ScopedJankInjectionEnabler::~ScopedJankInjectionEnabler() {
DCHECK(g_jank_enabled_for_test);
g_jank_enabled_for_test = false;
}
JankInjector::JankInjector() {
if (IsJankInjectionEnabled()) {
config_.target_dropped_frames_percent =
base::GetFieldTrialParamByFeatureAsInt(
features::kJankInjectionAblationFeature,
kJankInjectionTargetPercent, config_.target_dropped_frames_percent);
config_.dropped_frame_cluster_size = base::GetFieldTrialParamByFeatureAsInt(
features::kJankInjectionAblationFeature, kJankInjectionClusterSize,
config_.dropped_frame_cluster_size);
}
}
JankInjector::~JankInjector() = default;
bool JankInjector::IsEnabled(const GURL& url) {
return IsJankInjectionEnabled() && IsJankInjectionEnabledForURL(url);
}
void JankInjector::ScheduleJankIfNeeded(
const viz::BeginFrameArgs& args,
base::SingleThreadTaskRunner* task_runner) {
if (ShouldJankCurrentFrame(args)) {
ScheduleJank(args, task_runner);
did_jank_last_time_ = true;
} else {
++total_frames_;
did_jank_last_time_ = false;
}
}
bool JankInjector::ShouldJankCurrentFrame(
const viz::BeginFrameArgs& args) const {
// If jank was injected during the previous frame, then do not inject jank
// again now.
if (did_jank_last_time_)
return false;
// Do not jank during the first frame.
if (!total_frames_)
return false;
auto current_jank = janked_frames_ * 100 / total_frames_;
// Do not drop any more frames if the injected jank is already above or at the
// target.
if (current_jank >= config_.target_dropped_frames_percent)
return false;
// If janking now makes the dropped the frames goes beyond the target, then do
// not inject the jank yet.
auto next_jank = (janked_frames_ + config_.dropped_frame_cluster_size) * 100 /
(total_frames_ + config_.dropped_frame_cluster_size);
if (next_jank > config_.target_dropped_frames_percent)
return false;
return true;
}
void JankInjector::ScheduleJank(const viz::BeginFrameArgs& args,
base::SingleThreadTaskRunner* task_runner) {
JankInjectionParams params;
params.jank_duration = config_.dropped_frame_cluster_size * args.interval;
params.busy_loop = true;
task_runner->PostTask(FROM_HERE, base::BindOnce(&RunJank, std::move(params)));
janked_frames_ += config_.dropped_frame_cluster_size;
total_frames_ += config_.dropped_frame_cluster_size;
}
} // namespace cc