本讲是Android Camera性能分析专题的第27讲 ，我们介绍CameraServer Request Latency，包括如下内容：
- Request Latency是什么
- Request Latency配置
- Request Latency实战
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Request Latency是什么
Request Latency用于衡量HAL执行processBatchCaptureRequests的耗时。
影响:
- 如果该耗时太长，会拉低CaptureRequest的帧率，需要从HAL角度分析
Request Latency配置
Request Latency直方图配置
-
分成10份（默认值）， 间隔为40ms
-
static const int32_t kRequestLatencyBinSize = 40; // in ms
添加Sample的时机
- 在每次调用HAL的processCaptureRequest接口时，会统计其耗时，然后作为一个Sample添加到CameraLatencyHistogram
Request Latency实战
- 代码讲解
nsecs_t tRequestStart = systemTime(SYSTEM_TIME_MONOTONIC);
submitRequestSuccess = sendRequestsBatch();
nsecs_t tRequestEnd = systemTime(SYSTEM_TIME_MONOTONIC);
mRequestLatency.add(tRequestStart, tRequestEnd);- 实战演示：在CameraLatencyHistogram增加Samples总的平均耗时
void CameraLatencyHistogram::add(nsecs_t start, nsecs_t end) {
nsecs_t duration = end - start;
int32_t durationMs = static_cast<int32_t>(duration / 1000000LL);
int32_t binIndex = durationMs / mBinSizeMs;
if (binIndex < 0) {
binIndex = 0;
} else if (binIndex >= mBinCount) {
binIndex = mBinCount-1;
}
mBins[binIndex]++;
mTotalCount++;
mTotoalDuration += duration;
}打印Log时：
void CameraLatencyHistogram::log(const char* fmt, ...) {
if (mTotalCount == 0) {
return;
}
va_list args;
va_start(args, fmt);
String8 histogramName = String8::formatV(fmt, args);
ALOGI("%s (%" PRId64 ") samples, avg(%.2f ms):", histogramName.string(), mTotalCount, (float)(mTotoalDuration/1e6) / mTotalCount);
va_end(args);
String8 lineBins, lineBinCounts;
formatHistogramText(lineBins, lineBinCounts);
ALOGI("%s", lineBins.c_str());
ALOGI("%s", lineBinCounts.c_str());
}
