第26讲 DequeueBuffer Latency - Android Camera性能分析

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:

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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);
  • 实战演示,请参阅视频

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