linux-kernel - taskstats and /proc/.../io asymmetry?

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Message-ID: <482AC60D.8020207@hp.com>
Date:	Wed, 14 May 2008 06:59:25 -0400
From:	Mark Seger <Mark.Seger@...com>
To:	Shailabh Nagar <nagar@...son.ibm.com>,
	Balbir Singh <balbir@...ibm.com>, Jes Sorensen <jes@....com>,
	Chris Sturtivant <csturtiv@....com>, Tony Ernst <tee@....com>,
	Guillaume Thouvenin <guillaume.thouvenin@...l.net>,
	Jay Lan <jlan@...r.sgi.com>, linux-kernel@...r.kernel.org
Subject: taskstats and /proc/.../io asymmetry?

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

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