linux-kernel - Re: [RFC][PATCH] sched: cpuacct: Track cpuusage per cpu frequency

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Message-ID: <20100406021559.GD3630@balbir.in.ibm.com>
Date:	Tue, 6 Apr 2010 07:45:59 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Mike Chan <mike@...roid.com>, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] sched: cpuacct: Track cpuusage per cpu frequency

* menage@...gle.com <menage@...gle.com> [2010-04-05 12:52:57]:

> On Mon, Apr 5, 2010 at 12:33 PM, Mike Chan <mike@...roid.com> wrote:
> > New file: cpuacct.cpufreq when CONFIG_CPU_FREQ_STATS is enabled.
> >
> > cpuacct.cpufreq accounts for cpu time per-cpu frequency, time is exported
> > in nano-seconds
> 
> Can you clarify the wording of this (and describe it in the relevant
> Documentation/... file)? It's not clear.
> 
> From the code, it appears that the file reports a breakdown of how
> much CPU time the cgroup has been consuming at each different CPU
> frequency level. If so, then you probably want to reword the
> description to avoid "per-cpu", since that makes it sounds as though
> it's reporting something, well, "per CPU".
> 
> Also, what's the motivation here? If it's for power monitoring
> purposes, might it be simpler to just report a single number, that's
> the integral of the CPU usage by frequency index (i.e. calculated from
> the same information that this patch is already gathering in
> cpuacct_charge()) rather than dumping a whole table on userspace?

As utilization increases, won't the integral quickly overflow? BTW,
Mike have you looked at the scaled accounting infrastructure we have
in taskstats?

-- 
	Three Cheers,
	Balbir
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