Re: [Xen-devel] Request for help, implementing a new network scheduler

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

On 03/02/15 00:42, Ronald PIna wrote:
> Hi
>
> I am working for the msc thesis to improve the performance on network
> for guest domains that uses real-time services like voip or video
> streaming servers , i have an idea to implement a network scheduler on
> network backend, the schedulers may be weighted fair queuing or weighted
> round robin,  the idea is to schedule first the packet coming from
> real-time guest services, one of those schedulers could make the job and
> can prioritize the network traffic.
>
> As far as i have studied from previous works explain that the outgoing
> network traffic in xen is scheduled in round robin manner inside the
> function net_tx_action(). Later on the last version of xen this function
> has changed xenvif_tx_action() and have changed his primarily structure.
> My primarily goal is to modify the round robin to more advanced
> scheduler  which introduce priorities. The clear question is that where
> is located the function which schedule in round robin and if possible
> are there any concern about using another network scheduling method in
> netback ?
xenvif_tx_action is called from NAPI polling context, per queue. It 
copies & maps the packets from the guest to Dom0 (at which point it 
doesn't have the slightest idea about the packet content), formats them 
in xenvif_tx_submit to be a well formed skb, and calls netif_receive_skb 
to hand it over to the stack.
You could try doing some reordering in xenvif_tx_submit or introducing 
priorities in the ring buffer, but I would strongly discourage you to do 
that, for similar reasons mentioned by Ian. You would be better off 
using standard Linux tools for doing that, see 'man tc', and I would try 
on the sending side, in the guest, before netfront gets the packet.
Or, if your idea is to prioritize between traffic coming from separate 
guests, then xenvif_tx_action is definitely the wrong place to do that: 
as said above, it deals only with the traffic of one particular queue of 
a netback device. You might want to look into the entity 
switching/routing between the guests and NICs: Linux bridge module, 
openvswitch, the IP routing engine of the backend etc. I think the first 
two could be the reasonable choices, bridge might lacks such 
functionality though.
Zoli


> Thanks in advance
>
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