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Re: [Xen-devel] Regarding TX/RX rings

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Regarding TX/RX rings
From: Mahendra Kutare <mahendra.kutare@xxxxxxxxx>
Date: Sat, 23 Oct 2010 08:19:27 -0400
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On Fri, Oct 22, 2010 at 9:03 PM, James Harper <james.harper@xxxxxxxxxxxxxxxx> wrote:
> Hi All,
> I have to monitor the rate of data transfer over a time window for TX/RX rings
> in DOM0 for all DOMUs.
> Is there a good place to start with in terms of code ? Any pointers of sample
> implementation already existing for this will be useful.

For what purpose?

Why monitor the rings directly rather than monitoring throughput at a level that already allows such things (disk io / network io etc)?

Would you be monitoring rings slots used or actual data?

There appears to be data available in /sys/devices/vbd-<domid>-<devid> that might tell you what you want for vbd's (at least there is in - your kernel might be different). That may correlate directly to rings slots or may be an abstraction. Vbd only has one ring containing both read and write requests but the stats seem to break it down.

For network you can find throughput information in the /sys/devices/vif-<domid>-<devid>/net:vif<domid>.<devid>/statistics (maybe a few ways to get there) but that seems more packet oriented, and a single packet doesn't correlate directly to a ring slot - you could have 1 packet taking several rings slots and for GSO you could have a 'large' packet in one ring slot that would be broken up into several MTU sized packets. You'd probably need to implement a similar statistics reporting function in vif like vbd to tell you what you want to know about the actual rings.


The reason I am looking to monitor these rings is to find the variability of the data transfer through the TX/RX rings i.e. inbound/outbound network traffic. I am doing variability analysis for various combination of VMs running in Xen. I am looking at both CPU and Network level metrics. The goal is to infer characteristics looking at these lower level metrics about the VMs running.

On my current installation of Xen 3.4.3 with kernel ,  the data mentioned in /sys/devices/vbd- or /sys/devices/vif is not available. I need to upgrade my kernel.

I have seen that if I monitor the network traffic input and output throughput data (through say xentop running application - RUBiS) it does not really vary a lot. So I want to monitor the lower levels to see if there exists variability that eventually evens out.

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