本讲是Android Camera性能分析专题的第26讲 ​，我们介绍DequeueBuffer Latency，包括如下内容：

1. DequeueBuffer Latency是什么
2. DequeueBuffer Latency配置
3. DequeeuBuffer Latency实战

视频在线观看：

• 极客笔记：
  极客笔记在线课程

加入知识星球与更多Camera同学交流
– 星球名称：深入浅出Android Camera
– 星球ID: 17296815
– Wechat: 极客笔记圈

DequeueBuffer Latency是什么

DequeueBuffer Latency 用于衡量/记录从BufferQueue里面获取Buffer的耗时。

影响：

• 如果该耗时太长，会拉低CaptureRequest的帧率，具体体现在送给HAL的CaptureRequest速度变慢。

每一个Camera3OutputStream都会统计DequeueBuffer Latency。

• 这里的Output/Input Stream是相对HAL而言，HAL输出的流是Output Stream，输入给HAL的流是Input Stream

DequeueBuffer：

• 通过GraphicBufferProducer从BufferQueue里面获取一张未使用的Buffer

DequeueBuffer Latency配置

DequeueBuffer Latency直方图配置

• 分成10份（默认值），间隔为5ms

• static const int32_t kDequeueLatencyBinSize = 5; // in ms

添加Sample的时机

• 在每个CaptureRequest的prepareHalRequests中会调用getBuffer，进而触发到对BufferQueue的DequeueBuffer操作。

• Camera3OutputStream会对每次dequeueBuffer操作耗时做记录，然后作为一个Sample添加到CameraLatencyHistogram。

DequeeuBuffer Latency实战

• 代码讲解

  nsecs_t dequeueStart = systemTime(SYSTEM_TIME_MONOTONIC);size_t batchSize = mBatchSize.load();
  if (batchSize == 1) {sp anw = consumer;res = anw->dequeueBuffer(anw.get(), anb, fenceFd);
  } else {std::unique_lock batchLock(mBatchLock);res = OK;if (mBatchedBuffers.size() == 0) {if (remainingBuffers == 0) {ALOGE("%s: cannot get buffer while all buffers are handed out", __FUNCTION__);return INVALID_OPERATION;}if (batchSize > remainingBuffers) {batchSize = remainingBuffers;}batchLock.unlock();// Refill batched buffersstd::vector batchedBuffers;batchedBuffers.resize(batchSize);res = consumer->dequeueBuffers(&batchedBuffers);batchLock.lock();if (res != OK) {ALOGE("%s: batch dequeueBuffers call failed! %s (%d)",__FUNCTION__, strerror(-res), res);} else {mBatchedBuffers = std::move(batchedBuffers);}}if (res == OK) {// Dispatch batch buffers*anb = mBatchedBuffers.back().buffer;*fenceFd = mBatchedBuffers.back().fenceFd;mBatchedBuffers.pop_back();}
  }nsecs_t dequeueEnd = systemTime(SYSTEM_TIME_MONOTONIC);
  mDequeueBufferLatency.add(dequeueStart, dequeueEnd);

• 实战演示，请参阅视频