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

Thanks Zoli for your clear and very helpfull answer, my idea is to prioritize traffic that comes from different guest, for example if guest_1 is used for a voip server than it would be reasonable to schedule first the vif guest_1 before other guests. The diagram atached below explains better my idea. The goal is to improve the latency and jitter for real-time traffic which have critical requirements to QoS especially on heavy network i/o hosts, and if the vifs of different guest are scheduled on round robin manner in dom0 backend than we can improve this scheduling algorithm like using weighted round robin which can give more scheduling time to a vif that was used by a Âvoip-server guest. I would like to know that which module or function is responsible for scheduling vif on dom0 ?

Ronald     Â

On Tue, Feb 3, 2015 at 12:54 PM, Zoltan Kiss <zoltan.kiss@xxxxxxxxxx> wrote:

On 03/02/15 00:42, Ronald PIna wrote:

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.


Thanks in advance

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