第28讲 buffer limit latency -凯发k8手机登录

本讲是android camera性能分析专题的第28讲，我们介绍cameraserver buffer limit latency，包括如下内容：

1. buffer limit latency是什么
2. buffer limit latency配置
3. buffer limit latency实战

buffer limit latency是什么

buffer limit latency用于衡量当某路stream dequeue buffer数量达到producer的最大值后，等待hal处理的耗时。

什么是numoutstandingbuffers

• 已经送给hal，hal正在处理，未返回的buffer数量
• 视频讲解演示如何查看每路stream的numoutstandingbuffers

什么是camera_stream::max_buffers

• camera hal配置的，在未返回buffer的情况下，最多dequeuebuffer的数量
• 视频讲解演示如何查看每路stream hal配置的最大max_buffers

buffer limit latency配置

buffer limit latency直方图配置

• 分成10份（默认值）， 间隔为33ms
  • static const int32_t kbufferlimitlatencybinsize = 33; //in ms
  • latency histogram of the wait time for handout buffer count to drop below max_buffers.

添加sample的时机

• 当numoutstandingbuffers等于camera_stream::max_buffers时，会等待新的buffer返回，该latency衡量的是这个等待时间

buffer limit latency实战

// wait for new buffer returned back if we are running into the limit.
size_t numoutstandingbuffers = gethandoutoutputbuffercountlocked();
if (numoutstandingbuffers == camera_stream::max_buffers) {
    alogv("%s: already dequeued max output buffers (%d), wait for next returned one.",
                    __function__, camera_stream::max_buffers);
    nsecs_t waitstart = systemtime(system_time_monotonic);
    if (waitbuffertimeout < kwaitforbufferduration) {
        waitbuffertimeout = kwaitforbufferduration;
    }
    res = moutputbufferreturnedsignal.waitrelative(mlock, waitbuffertimeout);
    nsecs_t waitend = systemtime(system_time_monotonic);
    mbufferlimitlatency.add(waitstart, waitend);
    if (res != ok) {
        if (res == timed_out) {
            aloge("%s: wait for output buffer return timed out after %lldms (max_buffers %d)",
                    __function__, waitbuffertimeout / 1000000ll,
                    camera_stream::max_buffers);
        }
        return res;
    }
    size_t updatednumoutstandingbuffers = gethandoutoutputbuffercountlocked();
    if (updatednumoutstandingbuffers >= numoutstandingbuffers) {
        aloge("%s: outsanding buffer count goes from %zu to %zu, "
                "getbuffer(s) call must not run in parallel!", __function__,
                numoutstandingbuffers, updatednumoutstandingbuffers);
        return invalid_operation;
    }
}