introduce option of including non-hot startup methods

Summary:
Android on-device dexlayout optimization takes non-hot startup only methods from baseline profile and lump them together into one section
LayoutType::kLayoutTypeStartupOnly. This presumably achieves better code locality and since ART does madvise on this section during dex layout, it reduces page faults during app's startup as well.
see ART code for ref:
https://fburl.com/androiddexlayout

Reviewed By: NTillmann

Differential Revision: D48794443

fbshipit-source-id: bdcbd25c1d383506569724d21f3d8e60f304c37a

opt/art-profile-writer/ArtProfileWriterPass.cpp

@@ -52,8 +52,15 @@ void ArtProfileWriterPass::bind_config() {
        m_perf_config.call_count_threshold);
   bind("perf_coldstart_appear100_threshold", m_perf_config.appear100_threshold,
        m_perf_config.coldstart_appear100_threshold);
+  bind("perf_coldstart_appear100_nonhot_threshold",
+       m_perf_config.coldstart_appear100_threshold,
+       m_perf_config.coldstart_appear100_nonhot_threshold);
   bind("perf_interactions", m_perf_config.interactions,
        m_perf_config.interactions);
+  after_configuration([this] {
+    always_assert(m_perf_config.coldstart_appear100_nonhot_threshold <
+                  m_perf_config.coldstart_appear100_threshold);
+  });
 }
 
 void ArtProfileWriterPass::run_pass(DexStoresVector& stores,
@@ -65,18 +72,27 @@ void ArtProfileWriterPass::run_pass(DexStoresVector& stores,
     bool startup = interaction_id == "ColdStart";
     const auto& method_stats = method_profiles.method_stats(interaction_id);
     for (auto&& [method, stat] : method_stats) {
+      // for startup interaction, we can include it into baseline profile
+      // as non hot method if the method appear100 is above nonhot_threshold
       if (stat.appear_percent >=
-              (startup ? m_perf_config.coldstart_appear100_threshold
+              (startup ? m_perf_config.coldstart_appear100_nonhot_threshold
                        : m_perf_config.appear100_threshold) &&
           stat.call_count >= m_perf_config.call_count_threshold) {
         auto& mf = method_flags[method];
-        mf.hot = true;
+        mf.hot = startup ? stat.appear_percent >
+                               m_perf_config.coldstart_appear100_threshold
+                         : true;
         if (startup) {
           // consistent with buck python config in the post-process baseline
           // profile generator, which is set both flags true for ColdStart
           // methods
           mf.startup = true;
-          mf.not_startup = true;
+          // if startup method is not hot, we do not set its not_startup flag
+          // the method still has a change to get it set if it appears in other
+          // interactions' hot list. Remember, ART only uses this flag to guide
+          // dexlayout decision, so we don't have to be pedantic to assume it
+          // never gets exectued post startup
+          mf.not_startup = mf.hot;
         } else {
           mf.not_startup = true;
         }

opt/art-profile-writer/ArtProfileWriterPass.h

@@ -26,16 +26,22 @@ class ArtProfileWriterPass : public Pass {
     float appear100_threshold;
     float call_count_threshold;
     float coldstart_appear100_threshold;
+    // Threshold to include a coldstart method in the profile,
+    // but not as a hot method. This threshold must be lower than
+    // coldstart_appear100_threshold.
+    float coldstart_appear100_nonhot_threshold;
     std::vector<std::string> interactions{"ColdStart"};
 
     PerfConfig()
         : appear100_threshold(101.0),
           call_count_threshold(0),
-          coldstart_appear100_threshold(80.0) {} // Default: off
-    PerfConfig(float a, float c, float ca)
+          coldstart_appear100_threshold(80.0),
+          coldstart_appear100_nonhot_threshold(50.0) {} // Default: off
+    PerfConfig(float a, float c, float ca, float can)
         : appear100_threshold(a),
           call_count_threshold(c),
-          coldstart_appear100_threshold(ca) {}
+          coldstart_appear100_threshold(ca),
+          coldstart_appear100_nonhot_threshold(can) {}
   };
 
   PerfConfig m_perf_config;