Re: Linux Disk Performance/File IO per process

[Szabolcs Szakacsits <szaka@xxxxxxxxxxxx>]

On Mon, 29 Jan 2001, Chris Evans wrote:

> Stephen Tweedie has a rather funky i/o stats enhancement patch which
> should provide what you need. It comes with RedHat7.0 and gives decent
> disk statistics in /proc/partitions.

Monitoring via /proc [not just IO but close to anything] has the
features:
 - slow, not atomic, not scalable
 - if kernel decides explicitely or due to a "bug" to refuse doing
   IO, you get something like this [even using a mlocked, RT monitor],
   procs                    memory    swap          io     system         cpu
 r  b  w   swpd  free  buff  cache  si  so    bi    bo   in    cs  us  sy  id
 0  1  1  27116  1048   736 152832 128 1972 2544   869   44  1812   2  43  55
 5  0  2  27768  1048   744 153372  52 1308 2668   777   43  1772   2  61  37
 0  2  1  28360  1048   752 153900 332 564  2311   955   49  2081   1  68  31
<frozen>
 1  7  2  28356  1048   752 153708 3936  0  2175 29091  494 27348   0   1  99
 1  0  2  28356  1048   792 153656 172   0  7166     0  144   838   4  17  80

In short, monitoring via /proc is unreliable.

        Szaka