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Commit a517e9e3 authored by Sadrul Chowdhury's avatar Sadrul Chowdhury
Browse files

Boost process priority during fork. 

The zygote process sets MAX priority for the child process after a
fork if it is a 'high priority fork' (e.g. for top-app). However,
the zygote does a fair amount of work before the fork, and can take
up some amount of time due to getting descheduled. This introduces
latency in app-launch, especially on low-power devices.

Fix this by setting the zygote process priority to MAX for a
high-priority fork early on, and reset it back to DEFAULT
afterwards.

Bug: 323891634
Test: manually
Change-Id: Iac1ea81531f59ee6245c73530f2dd639209421f7
parent a0ce6b06

core/jni/com_android_internal_os_Zygote.cpp

+12 −0
Original line number Diff line number Diff line
@@ -2256,6 +2256,11 @@ pid_t zygote::ForkCommon(JNIEnv* env, bool is_system_server, 
                         const std::vector<int>& fds_to_ignore,

                         bool is_priority_fork,

                         bool purge) {

  ATRACE_CALL();

  if (is_priority_fork) {

    setpriority(PRIO_PROCESS, 0, PROCESS_PRIORITY_MAX);

  }



  SetSignalHandlers();



  // Curry a failure function.
@@ -2341,6 +2346,10 @@ pid_t zygote::ForkCommon(JNIEnv* env, bool is_system_server, 
  // We blocked SIGCHLD prior to a fork, we unblock it here.

  UnblockSignal(SIGCHLD, fail_fn);



  if (is_priority_fork && pid != 0) {

    setpriority(PRIO_PROCESS, 0, PROCESS_PRIORITY_DEFAULT);

  }



  return pid;

}
@@ -2408,6 +2417,7 @@ static jint com_android_internal_os_Zygote_nativeForkSystemServer( 
        JNIEnv* env, jclass, uid_t uid, gid_t gid, jintArray gids,

        jint runtime_flags, jobjectArray rlimits, jlong permitted_capabilities,

        jlong effective_capabilities) {

  ATRACE_CALL();

  std::vector<int> fds_to_close(MakeUsapPipeReadFDVector()),

                   fds_to_ignore(fds_to_close);
@@ -2483,6 +2493,7 @@ static jint com_android_internal_os_Zygote_nativeForkApp(JNIEnv* env, 
                                                         jintArray managed_session_socket_fds,

                                                         jboolean args_known,

                                                         jboolean is_priority_fork) {

  ATRACE_CALL();

  std::vector<int> session_socket_fds =

      ExtractJIntArray(env, "USAP", nullptr, managed_session_socket_fds)

          .value_or(std::vector<int>());
@@ -2498,6 +2509,7 @@ int zygote::forkApp(JNIEnv* env, 
                    bool args_known,

                    bool is_priority_fork,

                    bool purge) {

  ATRACE_CALL();



  std::vector<int> fds_to_close(MakeUsapPipeReadFDVector()),

                   fds_to_ignore(fds_to_close);