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47 lines
2.9 KiB
47 lines
2.9 KiB
4 months ago
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logd can record and replay log messages for offline analysis.
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Recording Messages
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------------------
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logd has a `RecordingLogBuffer` buffer that records messages to /data/misc/logd/recorded-messages.
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It stores messages in memory until that file is accessible, in order to capture all messages since
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the beginning of boot. It is only meant for logging developers to use and must be manually enabled
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in by adding `RecordingLogBuffer.cpp` to `Android.bp` and setting
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`log_buffer = new SimpleLogBuffer(&reader_list, &log_tags, &log_statistics);` in `main.cpp`.
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Recording messages may delay the Log() function from completing and it is highly recommended to make
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the logd socket in `liblog` blocking, by removing `SOCK_NONBLOCK` from the `socket()` call in
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`liblog/logd_writer.cpp`.
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Replaying Messages
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------------------
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Recorded messages can be replayed offline with the `replay_messages` tool. It runs on host and
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device and supports the following options:
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1. `interesting` - this prints 'interesting' statistics for each of the log buffer types (simple,
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chatty, serialized). The statistics are:
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1. Log Entry Count
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2. Size (the uncompressed size of the log messages in bytes)
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3. Overhead (the total cost of the log messages in memory in bytes)
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4. Range (the range of time that the logs cover in seconds)
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2. `memory_usage BUFFER_TYPE` - this prints the memory usage (sum of private dirty pages of the
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`replay_messages` process). Note that the input file is mmap()'ed as RO/Shared so it does not
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appear in these dirty pages, and a baseline is taken before allocating the log buffers, so only
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their contributions are measured. The tool outputs the memory usage every 100,000 messages.
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3. `latency BUFFER_TYPE` - this prints statistics of the latency of the Log() function for the given
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buffer type. It specifically prints the 1st, 2nd, and 3rd quartiles; the 95th, 99th, and 99.99th
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percentiles; and the maximum latency.
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4. `print_logs BUFFER_TYPE [buffers] [print_point]` - this prints the logs as processed by the given
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buffer_type from the buffers specified by `buffers` starting after the number of logs specified by
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`print_point` have been logged. This acts as if a user called `logcat` immediately after the
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specified logs have been logged, which is particularly useful since it will show the chatty
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pruning messages at that point. It additionally prints the statistics from `logcat -S` after the
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logs.
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`buffers` is a comma separated list of the numeric buffer id values from `<android/log.h>`. For
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example, `0,1,3` represents the main, radio, and system buffers. It can can also be `all`.
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`print_point` is an positive integer. If it is unspecified, logs are printed after the entire
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input file is consumed.
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5. `nothing BUFFER_TYPE` - this does nothing other than read the input file and call Log() for the
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given buffer type. This is used for profiling CPU usage of strictly the log buffer.
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