linux-kernel - Re: RFC: /proc/<pid>/sched should contain cumulative data for all threads in process

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Date:	Tue, 8 Feb 2011 13:11:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Chris Friesen <chris.friesen@...band.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RFC: /proc/<pid>/sched should contain cumulative data for all
 threads in process


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, 2011-02-07 at 16:29 -0600, Chris Friesen wrote:
> > Hi,
> > 
> > We've got a tool that gathers lots of scheduling data for each process
> > (not task/thread) on the system.
> > 
> > For /proc/<pid>/{stat,io} this is straightforward, as the per-thread
> > values are summed together for the process as a whole.
> > 
> > However, /proc/<pid>/sched only shows the data for the individual thread
> > with the same tid as the pid.  To get a per-process view we need to
> > manually scan all the threads and sum them--and this can get expensive
> > due to all the extra file operations, parsing, etc.
> > 
> > Was this a concious design decision, or just an oversight?  Would a
> > patch converting it to whole-process values be accepted or is it enough
> > of a standard interface that we can't break existing apps that expect
> > the current behaviour?
> 
> I'd as soon remove all that stuff than extend it, its an abi liability,
> esp since you're talking about tools parsing this stuff.

So assuming a tool would want to capture such stats of the system, what would be its 
options? Could we do all this via system-wide counters and perf stat alike cheap, 
transparent gathering without having to patch/rebuild the kernel?

Thanks,

	Ingo
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