simpleperf: Delay processing ETM data until the buffer is half full

When using --decode-etm, the main thread is busy processing ETM data
and can miss flushing ETM data. To fix this, we can delay processing
ETM data after recording.

This patch triggers ETM data processing when the buffer is at least
half full. In the default configuration, the buffer is large enough
to hold ETM data for several seconds. So effectively, this delays
processing ETM data after recording.

Bug: 336375740
Test: run simpleperf_unit_test
Change-Id: Ib892aeea402773b1cab785f2c14886bb9f96d851

2 files changed, 13 insertions, 0 deletions

diff --git a/simpleperf/RecordReadThread.cpp b/simpleperf/RecordReadThread.cpp
index 2ab61278..2d034bc1 100644
--- a/simpleperf/RecordReadThread.cpp
+++ b/simpleperf/RecordReadThread.cpp
@@ -408,6 +408,7 @@ bool RecordReadThread::HandleAddEventFds(IOEventLoop& loop,
             success = false;
             break;
           }
+          has_etm_events_ = true;
         }
         cpu_map[fd->Cpu()] = fd;
       } else {
@@ -620,6 +621,9 @@ void RecordReadThread::PushRecordToRecordBuffer(KernelRecordReader* kernel_recor
 }
 
 void RecordReadThread::ReadAuxDataFromKernelBuffer(bool* has_data) {
+  if (!has_etm_events_) {
+    return;
+  }
   for (auto& reader : kernel_record_readers_) {
     EventFd* event_fd = reader.GetEventFd();
     if (event_fd->HasAuxBuffer()) {
@@ -659,6 +663,14 @@ void RecordReadThread::ReadAuxDataFromKernelBuffer(bool* has_data) {
 }
 
 bool RecordReadThread::SendDataNotificationToMainThread() {
+  if (has_etm_events_) {
+    // For ETM recording, the default buffer size is large enough to hold ETM data for several
+    // seconds. To reduce impact of processing ETM data (especially when --decode-etm is used),
+    // delay processing ETM data until the buffer is half full.
+    if (record_buffer_.GetFreeSize() >= record_buffer_.size() / 2) {
+      return true;
+    }
+  }
   if (!has_data_notification_.load(std::memory_order_relaxed)) {
     has_data_notification_ = true;
     char unused = 0;
diff --git a/simpleperf/RecordReadThread.h b/simpleperf/RecordReadThread.h
index c104b083..893f8234 100644
--- a/simpleperf/RecordReadThread.h
+++ b/simpleperf/RecordReadThread.h
@@ -211,6 +211,7 @@ class RecordReadThread {
   std::unique_ptr<std::thread> read_thread_;
   std::vector<KernelRecordReader> kernel_record_readers_;
   pid_t exclude_pid_ = -1;
+  bool has_etm_events_ = false;
 
   std::unordered_set<EventFd*> event_fds_disabled_by_kernel_;