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

To: "Mahendra Kutare" <mahendra.kutare@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Regarding TX/RX rings
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Sat, 23 Oct 2010 12:03:06 +1100
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Thread-topic: [Xen-devel] Regarding TX/RX rings
> 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.

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