where is /proc/<pid>/IO ??

[kornelix]

kernel 2.6.20 included new real-time process IO statistics.

Here is a fragment from the announcement:

So this IO accounting implements per-process statistics
of "storage I/O" (i.e.: I/O that _really_ does I/O on the storage device -
Linux already had I/O storage statistics but it's not per-task). The data
is reported through taskstats and procfs (/proc/$PID/io) (commit 1, 2, 3,
4, 5, 6, 7, 8, 10, 11)

I see no such thing in the several recent Linux distros I have tried out, with kernels up to 2.6.22. There are no /proc/<pid>/IO directories (I did see one of these, but the disk statistics were dead (small values that did not change)).

There must be something special I must do to enable this.
Where can I find information?

thanks
Mike

[markseger]

You have to build support into the kernel as it's not enabled by default and once you've done that you can display the stats in a format similar to 'ps' with collectl - see Process I/O Stats but that's not all collectl can do. See the home page to learn more.
-mark

[kornelix]

Thanks for the tip.

Why is this neat feature disabled by default? Is there an overhead problem? I cannot imagine why that would be the case.

[TetraFlash]

The new ubuntu scheduled for about 4 days from now comes with this feature enabled by default... I am currently using it to design a system resource monitor....

now the output for this io file is as follows
rchar: 296684
wchar: 237786
syscr: 2110
syscw: 1654
read_bytes: 516096
write_bytes: 348160
cancelled_write_bytes: 0

Does anyone know the meaning of all these... some of them seem self explanitory but a few make confused... and its not something that is easy to find a legend for because as you mentioned not many distros use it for who knows what reason.

[kornelix]

I just tried Ubuntu 8.04 and although the file /proc/<pid>/io is present, the data does not change even after thousands of disk accesses.

What gives? Are you using the server or desktop version? Mine is desktop.

[TetraFlash]

I have the same issue as do... I decided that watching the characters written and read (rchar and wchar which do increase) would help me identify a system hog as well... although not my ideal choice... its what im stuck doing at the moment.

if I needed access to this information on a 7.10 machine... how would I recompile the kernel to include this module???

[kornelix]

There are numerous documents on the web about how to compile a kernel, including one in the Ubuntu community web site. I have never tried it myself. I did read that to enable the process level I/O statistics all you have to do is set a #define switch and then compile. There is no other module that needs to be added.