linux-kernel - Re: [PATCH 0/4] Finer granularity and task/cgroup irq time accounting

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Message-ID: <20100824081407.GB27089@elte.hu>
Date:	Tue, 24 Aug 2010 10:14:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	Paul Turner <pjt@...gle.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 0/4] Finer granularity and task/cgroup irq time accounting


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

> On Thu, 2010-07-22 at 19:12 -0700, Venkatesh Pallipadi wrote:
> > >
> > > Well, the task and cgroup information is there but what does it really
> > > tell me? As long as the irq & softirq time can be caused by any other
> > > process I don't see the value of this incorrect data point.
> > >
> > 
> > Data point will be correct. How it gets used is a different qn. This
> > interface will be useful for Alert/Paranoid/Annoyed user/admin who
> > sees that the job exec_time is high but it is not doing any useful
> > work. 
> 
> I'm very sympathetic with Martin's POV. irq/softirq times per task 
> don't really make sense. In the case you provide above the solution 
> would be to subtract these times from the task execution time, not 
> break it out. In that case he would see his task not do much, and end 
> up with the same action list.

Right, andthis connects to something Frederic sent a few RFC patches for 
some time ago: finegrained irq/softirq perf stat support. If we do 
something in this area we need a facility that enables both types of 
statistics gathering.

Frederic's model is based on exclusion - so you could do a perf stat run 
that excluded softirq and hardirq execution from a workload's runtime. 
It's nifty, as it allows the reduction of measurement noise. (IRQ and 
softirq execution can be regarded as random noise added (or not added) 
to execution times)

Thanks,

	Ingo
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