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Re: [Xen-users] decreasing Xenmon overhead

To: "Diwaker Gupta" <diwaker.lists@xxxxxxxxx>
Subject: Re: [Xen-users] decreasing Xenmon overhead
From: "Ashish Gupta" <ashishgup@xxxxxxxxx>
Date: Tue, 29 May 2007 19:36:29 -0500
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Thanks Diwaker for your response and the great tool you have developed !

The dom0 util is 2-3 % without xenmon. In the normal ncurses mode with 1 second interval, the overhead is almost negligible. But at 100ms logging mode its much more as I said.  I am running a compute/communicate intensive app as one of the guests and trying to collect its stats at a sub-second level.

I am mainly interested in monitoring the cpu, block, waiting times for now, and possibly the number if IOs and execs per second also at a later stage. Do you think cutting down on events collected can greatly reduce the overhead ?
Also, is xentrace run as part of xenmon ? I am not absolutely clear where can I specify the event mask.

I am also wondering if writing the xenmon part in C or hard coding my requirements in xenbaked (for my purpose) could greatly reduce the overhead ? Any suggestions would be very helpful !


On 5/29/07, Diwaker Gupta <diwaker.lists@xxxxxxxxx> wrote:

> for offline analysis. However  I notice that at an interval of 100 ms or so
> the overhead imposed by dom0 is quite high , with upto 40% of CPU
> utilization.

Are you sure that the overhead is due to xenmon? What CPU utilization
do you see in Domain 0 for the same workload, but without xenmon?

>  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.

Exactly what metrics are you interested in monitoring? You might want
to look at 'xentrace --help' and 'xentrace -e'. Basically you want the
minimal set of events that will give you the desired information. To
see available events, look at /usr/include/xen/trace.h

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