commit f0bcc77dde3154c6681325bbfce95a0dcb6e834e
author Steven Moreland <smoreland@google.com> Tue Jan 19 19:59:05 2021 +0000
committer Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> Tue Jan 19 19:59:05 2021 +0000
tree d83ffb68514b03d1d5e233339da0d110f5f2ce6b
parent 4741328229fb0c2e1b4a55ef171e999e586aa3a0
parent 6d82be72227c9560fb60203c0691bf6cf54672e9

Merge "libbinder - avoid pthread_cond_broadcast per call" am: ff30b34cd2 am: dcb3e949ae am: 6d82be7222

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/1552572

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I70eca7ad29e9214d81bae8f13529f25f4642f267

libs/binder/IPCThreadState.cpp

diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index 2eee2c4..b038feb 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -489,12 +489,14 @@
 void IPCThreadState::blockUntilThreadAvailable()
 {
     pthread_mutex_lock(&mProcess->mThreadCountLock);
+    mProcess->mWaitingForThreads++;
     while (mProcess->mExecutingThreadsCount >= mProcess->mMaxThreads) {
         ALOGW("Waiting for thread to be free. mExecutingThreadsCount=%lu mMaxThreads=%lu\n",
                 static_cast<unsigned long>(mProcess->mExecutingThreadsCount),
                 static_cast<unsigned long>(mProcess->mMaxThreads));
         pthread_cond_wait(&mProcess->mThreadCountDecrement, &mProcess->mThreadCountLock);
     }
+    mProcess->mWaitingForThreads--;
     pthread_mutex_unlock(&mProcess->mThreadCountLock);
 }
 
@@ -534,7 +536,12 @@
             }
             mProcess->mStarvationStartTimeMs = 0;
         }
-        pthread_cond_broadcast(&mProcess->mThreadCountDecrement);
+
+        // Cond broadcast can be expensive, so don't send it every time a binder
+        // call is processed. b/168806193
+        if (mProcess->mWaitingForThreads > 0) {
+            pthread_cond_broadcast(&mProcess->mThreadCountDecrement);
+        }
         pthread_mutex_unlock(&mProcess->mThreadCountLock);
     }
 

libs/binder/ProcessState.cpp

diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index b5e4dfe..c38249e 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -399,6 +399,7 @@
     , mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
     , mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
     , mExecutingThreadsCount(0)
+    , mWaitingForThreads(0)
     , mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
     , mStarvationStartTimeMs(0)
     , mThreadPoolStarted(false)

libs/binder/include/binder/ProcessState.h

diff --git a/libs/binder/include/binder/ProcessState.h b/libs/binder/include/binder/ProcessState.h
index bab6469..2405ab6 100644
--- a/libs/binder/include/binder/ProcessState.h
+++ b/libs/binder/include/binder/ProcessState.h
@@ -107,11 +107,14 @@
             int                 mDriverFD;
             void*               mVMStart;
 
-            // Protects thread count variable below.
+            // Protects thread count and wait variables below.
             pthread_mutex_t     mThreadCountLock;
+            // Broadcast whenever mWaitingForThreads > 0
             pthread_cond_t      mThreadCountDecrement;
             // Number of binder threads current executing a command.
             size_t              mExecutingThreadsCount;
+            // Number of threads calling IPCThreadState::blockUntilThreadAvailable()
+            size_t              mWaitingForThreads;
             // Maximum number for binder threads allowed for this process.
             size_t              mMaxThreads;
             // Time when thread pool was emptied