taskstats and /proc/.../io asymmetry?

[Mark Seger <Mark.Seger@hp.com>]

If you look at /proc/pid/stat, you can get the total CPU consumed by a 
process.  If you look at /proc/pid/task/tid/stat you can get the cpu 
consumed by a thread and if the tid is that of the parent you only gets 
its consumption as opposed to all its children.

I was surprised to see that the way process I/O is reported doesn't 
follow this model.  There are no /prod/pid/task/tid/io entries but 
rather you need to look in /proc/tid/io.  While I view this as a minor 
inconvenience, I can certainly live with it.  However, /proc/pid/io does 
not show the aggregate I/O numbers for the whole process and that both 
surprises and disappoints.  This means if I have a process that starts a 
bunch of worker threads that do the real work and I want to find the top 
I/O consumers I can't simply walk the /proc/pid tree but rather have to 
look at all the threads of each process and add them up.

Or am I missing something?

-mark