Entender los contadores en/proc/[pid]/io

Question

Estoy creando un complemento para Munin para supervisar las estadísticas de los procesos nombrados. Una de las fuentes de información sería /proc/[pid]/io. Pero tengo dificultades para descubrir cuál es la diferencia entre rchar/wchar y read_bytes/written_bytes.

No son lo mismo, ya que proporcionan diferentes valores. ¿Qué representan?

Answer 1

Mientras que el proc manpage es lamentablemente detrás (y también lo son la mayoría de las páginas de manual/documentación sobre cualquier cosa no relacionados con el desarrollo del espacio de usuario de molde), esto es, afortunadamente, documentado por completo en el Linux kernel source bajo Documentation/filesystems/proc.txt. Aquí están los 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.