linux-kernel - Re: [PATCH 2/2] CFS CGroup: Report usage

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Message-ID: <6599ad830710251824w1e4a2720p90785e148b32f9c2@mail.gmail.com>
Date:	Thu, 25 Oct 2007 18:24:55 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	vatsa@...ux.vnet.ibm.com
Cc:	containers@...ts.linux-foundation.org,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] CFS CGroup: Report usage

On 10/23/07, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> wrote:
>
> agreed, we need to be reporting idle time in (milli)seconds, although
> the requirement we had was to report it back in percentage. I guess the
> percentage figure can be derived from the raw idle time number.
>
> How about:
>
>         idle time = t4-t3 (effectively sleep time)
>
> in the above example?
>
> > It doesn't seem quite right to me that a cgroup's idle time metric be
> > affected by the activity of other cgroups on the machine,
>
> I don't see how the idle time metric defined above (t4-t3) can be
> affected by other cgroup activity, unless the execution pattern of one
> cgroup is dependent on the others.

If the other cgroups are busier, and t1-t2 is longer, then the cgroup
will get to the point where it's ready to sleep later in wallclock
time, and t4-t3 will be shorter in absolute terms. If there were no
other cgroups running, then presumably the sleep time would actually
be the sum of those three periods.

Even so, I guess you're right that t4-t3 is the most appropriate thing
to report, as long as people realise that it's a bit of a fuzzy value.

> I think primarily for systems management tools to report back various
> statistics about a OpenVZ/VServer-like container (just like top reports stats
> for a OS currently). Let me check if there are other uses envisoned for
> it.

Sorry, I didn't mean "how will you report it to users?", I meant "what
kinds of useful information will the users be able to get from it?"

Paul
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