Hi Gilles,
Appreciate your response.
Pl find comments inline.
From: Gilles Chanteperdrix
To: makarand pradhan
Cc: "xenomai-core@gna.org"
Sent: Tuesday, October 25, 2011 4:50 AM
Subject: Re: [Xenomai-core] CPU utilization question
On 10/25/2011 12:19 AM, makarand pradhan wrote:
> (...) I'm
> assuming that the ROOT thread captures the %CPU spent in
> Linux/secnodary and each xenomai thread listed, captures the %CPU in
> primary domain. If a thread transitions to the secondary, then I'm
> assuming that the %util in secondary domain will get accounted
> against ROOT and the actual % usage in primary will get accounted
> against the thread.
You are assuming wrong, the CPU utilization measures the activity of the
linux kernel as a whole, including its idle task. So, the sum of all the
primary mode tasks and of the ROOT task is always 100%.
[MP]: Yes. I've noticed that the sum of all tasks is always 100. My question
was specifically about a xenomai task that transitions in secondary.
e.g. Assume a xenomai task that uses a total of 20% CPU. Of this assume that
10% is spent executing system calls in secondary domain and 10% is spent in the
primary domain. I believe that from an accounting perspective, 10% would get
accounted against ROOT and the xenomai task will show a CPU util of 10%. Is
this accurate?
> Question:
>
> If the linux process is sleeping, why do I see a CPU util against the
> process? Why is the CPU % util vary based on the activity I do in the
> primary domain?
rt_printf is a primary mode service which causes activity in secondary
mode: the actual printf is done by a plain linux task.
[MP]: Tx. It helped. I've taken the rt_printfs out and now my Linux process
that started the xenomai task shows 0% as expected.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
5136 root 20 0 4936 4372 3688 S 0.0 0.8 0:00.04 a.out
Rgds,
Makarand.
--
Gilles.___
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