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Re: [pcp] suitability of PCP for event tracing

To: Max Matveev <makc@xxxxxxxxx>
Subject: Re: [pcp] suitability of PCP for event tracing
From: Nathan Scott <nathans@xxxxxxxxxx>
Date: Sun, 19 Sep 2010 19:48:56 +1000 (EST)
Cc: pcp@xxxxxxxxxxx, "Frank Ch. Eigler" <fche@xxxxxxxxxx>, systemtap@xxxxxxxxxxxxxxxxxx, Ken McDonell <kenj@xxxxxxxxxxxxxxxx>
In-reply-to: <19605.55193.103255.767198@xxxxxxxxxxxx>
----- "Max Matveev" <makc@xxxxxxxxx> wrote:

> On Sun, 19 Sep 2010 00:21:34 +1000, Ken McDonell wrote:
> 
>  kenj> On 17/09/2010 9:18 AM, nathans@xxxxxxxxxx wrote:
> 
>  kenj> For the existing tools, I think we'll probably end up adding a
>  kenj> routine to libpcp to turn a PM_TYPE_EVENT "blob" into a
>  kenj> pmResult ... this will work for pminfo and pmprobe where the
>  kenj> timestamps are ignored.  For pmie, pmval, pmdumptext, pmchart,
>  kenj> ... I'm not sure how they can make sense of the event trace
>  kenj> data in real time, expecting data from time t, and getting a
>  kenj> set of values with different timestamps smaller than t is
> going
>  kenj> to be a bit odd for these ones.
> 
> I've been trying to come up with the use-case where event data and
> statistical data could be useful in the live mode (current tools
> issue
> aside) and I cannot really see one - Nathan or Frank, what did you
> have in mind?

One example was mentioned earlier - http://www.bootchart.org/
I'd want to extend it well beyond that use case though.

>  kenj> Plus several variants around lists per client or bit maps per
> client to 
>  kenj> reduce matching overhead on each pmFetch.
> 
> How would per-client list entries be trimmed?

Yeah, thats pretty much what I was wondering.  Have to at least ensure
memory use is bounded and small, and really can't have memory utilisation
dependent on number of clients, IMO.

cheers.

-- 
Nathan

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