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

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Date:	Tue, 08 Feb 2011 10:21:05 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RFC: /proc/<pid>/sched should contain cumulative data for all
 threads in process

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.

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