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Re: [Xen-users] decreasing Xenmon overhead

To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Subject: Re: [Xen-users] decreasing Xenmon overhead
From: "Ashish Gupta" <ashishgup@xxxxxxxxx>
Date: Wed, 30 May 2007 22:14:26 -0500
Cc: Mark Williamson <mark.williamson@xxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
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These are some great points.

As you said earlier, is 100 ms resolution meaningless ? Does it mean that the data emitted by xentrace is not accurate enough at that level ?

So, I would have to do all the processing of xenbaked and xenmon in one module offline, over the xentrace data. Does this seem like a fair approach ?


On 5/30/07, Petersson, Mats <Mats.Petersson@xxxxxxx> wrote:

> -----Original Message-----
> From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On
> Behalf Of Mark Williamson
> Sent: 30 May 2007 13:11
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Cc: Petersson, Mats; Ashish Gupta
> Subject: Re: [Xen-users] decreasing Xenmon overhead
> > > Are there ways I can drastically reduce this overhead ? I
> > > read somwhere about event overhead, using event masks and
> > > python overhead,  but am not really sure how to use this
> > > information to reduce the overhead.
> >
> > Perhaps write a C-program rather than using Python to
> fetch/format the
> > information? That shouls improve it, but I guess you'll still see a
> > noticable overhead if you sample the information every 100ms.
> xentrace (for instance) just logs out data to a file, and
> does the formatting
> offline using a python script.  This is also a useful
> approach if you're
> getting data out at a high bandwidth.

Very good point. Just "storing" the data in a trivial format is much
less CPU-intensive than doing a lot of processing for each process step.
And hopefully, when you've finished the testing/logging, you don't care
as much about how big the load is on the system.

> Cheers,
> Mark
> --
> Dave: Just a question. What use is a unicyle with no seat?
> And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!

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