Are there NIC emulations in the kernel with built-in rate limiting? Or
is that supposed to be strictly the province of qdiscs/filters?
I've been messing about with netperf in a VM using virtio_net, to which
rate limiting has been applied to its corresponding vnetN interface -
rate policing on vnetN ingress (the VM's outbound) and htb on the vnetN
egress (the VM's inbound).
Looking at the "demo mode" output of netperf and a VM throttled to 800
Mbit/s in each direction I see that inbound to the VM is quite steady
over time - right at about 800 Mbit/s. However, looking at that same
sort of data for outbound from the VM shows considerable variability
ranging anywhere from 700 to 900 Mbit/s (though the bulk of the
variability is clustered more like 750 to 850.
I was thinking that part of the reason may stem from the lack of direct
feedback to the VM since the policing is on the vnetN interface and
wondered if it might be "better" if the VM's outbound network rate were
constrained not by an ingress policing filter on the vnetN interface but
by the host/hypervisor/emulator portion of the NIC and how quickly it
pulls packets from the tx queue. That would allow the queue which
built-up to be in the VM itself and would more accurately represent what
a "real NIC" of that bandwidth would do.
happy benchmarking,
rick jones
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