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diff --git a/libnetdata/procfile/README.md b/libnetdata/procfile/README.md new file mode 100644 index 0000000..3eeb1e2 --- /dev/null +++ b/libnetdata/procfile/README.md @@ -0,0 +1,67 @@ +<!-- +title: "PROCFILE" +custom_edit_url: https://github.com/netdata/netdata/edit/master/libnetdata/procfile/README.md +--> + +# PROCFILE + +procfile is a library for reading text data files (i.e `/proc` files) in the fastest possible way. + +## How it works + +The library automatically adapts (through the iterations) its memory so that each file +is read with single `read()` call. + +Then the library splits the file into words, using the supplied separators. +The library also supported quoted words (i.e. strings within of which the separators are ignored). + +### Initialization + +Initially the caller: + +- calls `procfile_open()` to open the file and allocate the structures needed. + +### Iterations + +For each iteration, the caller: + +- calls `procfile_readall()` to read updated contents. + This call also rewinds (`lseek()` to 0) before reading it. + + For every file, a [BUFFER](/libnetdata/buffer/README.md) is used that is automatically adjusted to fit the entire + file contents of the file. So the file is read with a single `read()` call (providing atomicity / consistency when + the data are read from the kernel). + + Once the data are read, 2 arrays of pointers are updated: + + - a `words` array, pointing to each word in the data read + - a `lines` array, pointing to the first word for each line + + This is highly optimized. Both arrays are automatically adjusted to + fit all contents and are updated in a single pass on the data. + + The library provides a number of macros: + + - `procfile_lines()` returns the # of lines read + - `procfile_linewords()` returns the # of words in the given line + - `procfile_word()` returns a pointer the given word # + - `procfile_line()` returns a pointer to the first word of the given line # + - `procfile_lineword()` returns a pointer to the given word # of the given line # + +### Cleanup + +When the caller exits: + +- calls `procfile_free()` to close the file and free all memory used. + +### Performance + +- a **raspberry Pi 1** (the oldest single core one) can process 5.000+ `/proc` files per second. +- a **J1900 Celeron** processor can process 23.000+ `/proc` files per second per core. + +To achieve this kind of performance, the library tries to work in batches so that the code +and the data are inside the processor's caches. + +This library is extensively used in Netdata and its plugins. + +[](<>) |