Informazioni sui contatori in/proc/[pid]/io

Question

Sto creando un plug-in per Munin per monitorare le statistiche dei processi denominati. Una delle fonti di informazioni sarebbe /proc/[pid]/io. Ma ho difficoltà a scoprire quale sia la differenza tra rchar/wchar e read_bytes/written_bytes.

Non corrispondono, poiché forniscono valori diversi. Cosa rappresentano?

Answer 1

Mentre il proc manpage è tristemente dietro (e lo sono anche la maggior parte delle pagine di manuale/documentazione su qualsiasi cosa non in materia di cookie-cutter sviluppo user-space), questa roba è fortunatamente documentato completamente nel Linux kernel source sotto Documentation/filesystems/proc.txt. Qui ci sono i bit rilevanti:

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.