Merge "libbinder - avoid pthread_cond_broadcast per call"

3 files changed, 13 insertions, 2 deletions

diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index 2eee2c40a3..b038feb878 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -489,12 +489,14 @@ void IPCThreadState::flushCommands()
 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 @@ status_t IPCThreadState::getAndExecuteCommand()
             }
             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);
     }
 
diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index b5e4dfe4df..c38249ef7c 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -399,6 +399,7 @@ ProcessState::ProcessState(const char *driver)
     , mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
     , mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
     , mExecutingThreadsCount(0)
+    , mWaitingForThreads(0)
     , mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
     , mStarvationStartTimeMs(0)
     , mThreadPoolStarted(false)
diff --git a/libs/binder/include/binder/ProcessState.h b/libs/binder/include/binder/ProcessState.h
index bab6469d12..2405ab6b9e 100644
--- a/libs/binder/include/binder/ProcessState.h
+++ b/libs/binder/include/binder/ProcessState.h
@@ -107,11 +107,14 @@ private:
             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