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O que significam os contadores em / proc / [pid] / io?

Estou criando um plugin para Munin para monitorar estatísticas de processos nomeados. Uma das fontes de informação seria /proc/[pid]/io . Mas tenho dificuldade em descobrir qual é a diferença entre rchar/wchar e read_bytes/written_bytes.

Eles não são os mesmos, pois fornecem valores diferentes. O que eles representam?

37
Kvisle

Enquanto o proc manpage está lamentavelmente atrasado (e também a maioria das páginas de manual/documentação sobre qualquer coisa que não esteja relacionada ao desenvolvimento do espaço do usuário do cookie-cutter), esse material é felizmente documentado completamente no kernel do Linux origem em Documentation/filesystems/proc.txt . Aqui estão os bits relevantes:

rchar
-----

I/O counter: chars read
The number of bytes which this task has caused to be read from storage. This
is simply the sum of bytes which this process passed to read() and pread().
It includes things like tty IO and it is unaffected by whether or not actual
physical disk IO was required (the read might have been satisfied from
pagecache)


wchar
-----

I/O counter: chars written
The number of bytes which this task has caused, or shall cause to be written
to disk. Similar caveats apply here as with rchar.


read_bytes
----------

I/O counter: bytes read
Attempt to count the number of bytes which this process really did cause to
be fetched from the storage layer. Done at the submit_bio() level, so it is
accurate for block-backed filesystems. <please add status regarding NFS and
CIFS at a later time>


write_bytes
-----------

I/O counter: bytes written
Attempt to count the number of bytes which this process caused to be sent to
the storage layer. This is done at page-dirtying time.
64
Matt Joiner