Re: [Xen-devel] Request for help: passing network statistics from netback driver to Xen scheduler.

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jul 31, 2014 at 07:12:55PM +0000, Dlugajczyk, Marcin wrote:
> 
> On 31 Jul 2014, at 18:38, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> 
> > Just as a comment: I think a potential problem with this approach is
> > that you'll run into a positive feedback loop.  Processing network
> > traffic takes a lot of CPU time; and in particular, it needs the
> > ability to process packets in a *timely* manner.  Because most
> > connections are TCP, the ability to do work now *creates* work later
> > (in the form of more network packets).  Not having enough CPU, or
> > being delayed in when it can process packets, even by 50ms, can
> > significantly reduce the amount of traffic a VM gets.  So it's likely
> > that a domain that currently has a high priority will be able to
> > generate more traffic for itself, maintaining its high priority; and a
> > domain that currently has a low priority will not be able to send acks
> > fast enough, and will continue to receive low network traffic, thus
> > maintaining its low priority.
> > 
> > Something to watch out for, anyway. :-)
> 
> Thank you for your feedback! Iâm aware of the potential problem. However, as 
> I have a tight deadline, 
> Iâll address the issue when it arises. 
> 
> > Does the printk print the new value (i.e., "Intensity now [nnn] for
> > domain M"), or just print that it's trying to do something (i.e.,
> > "Incrementing network intensityâ)?
> 
> Itâs printing the new value. The xenvif_rx_action function looks like that 
> after my modification:
> 
> void xenvif_rx_action(struct xenvif *vif)
> {
...
> }
> 

It's better to just paste in the diff instead of the whole function.
Also you will need to state clearly what version the diff is based on.

Wei.

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