第26讲 dequeuebuffer latency -凯发k8旗舰厅

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：

dequeuebuffer latency是什么
dequeuebuffer latency配置
dequeeubuffer latency实战

资源	描述
在线课程
知识星球	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是什么

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。

dequeuebuffer latency配置

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 buffers
      std::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);