[Xen-devel] doubt regarding IO scheduler and credit scheduling in netback

[Kuriakose Mathew <kmathew123@xxxxxxxxx>]

Hi,
With reference to the netback and netfront model of device
driver in Xen(specifically Xen 3.1.3 and linux 2.6.18.8-- I know it is a bit old but please excuse), I am confused as to where the
network IO scheduler fits in. I have read that there are different
types of IO schedulers in linux - deadline ,anticipatory, complete fair
queueing (cfq )etc. where cfq is the default. Is it only being used in
the context of disk IO? or the same thing is used for network IO?

Also (as a related doubt), in netback code(In netback.c net_tx_action ) , I saw some credit scheduling of the network
interfaces(netif_t *netif) corresponding to guest domains. So whenever
Dom 0 is scheduled ,it does a credit scheduling of the network
interfaces corresponding to different DomUs. The credits will get refreshed when the credit_timeout happens. The next network interface(netif) will be scheduled if the credits for the current netif is exhausted. Is my understanding correct ?
What are the other cases when the next netif is scheduled? (one would obviously be the case when there are no packets to send. Any other case?) When I did some experiments, I found that the bandwidth is fairly divided among all the domains. So there should be some mechasim to ensure this.

In this context where does
the IO scheduler fits in? 
Please explain.

Thanks
Kuriakose Mathew

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