[Cake] Possible BUG - parent backlog incorrectly updated in case of NET_XMIT_CN

[Eric Dumazet]

On Sun, 2016-06-12 at 20:51 +0300, Jonathan Morton wrote:
> > On 12 Jun, 2016, at 20:48, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> > 
> >> A) In my failing to make sense of all the dialog around these patches
> >> ( https://lwn.net/Articles/687617/  ), it sounds like this (inbound
> >> and outbound) processing are still locked to a single thread,
> >> essentially?
> > 
> > Om a router, these discussions should not matter really, since the
> > workload is about receiving/sending packets without user space
> > intervention (well... I do hope this !)
> 
> Dave’s point is that inbound and outbound processing could in
> principle be on *two* distinct threads, potentially doubling aggregate
> throughput in a CPU-limited environment.

Only if IRQ were not properly tuned (smp_affinity) on SMP host.

If you have one CPU, having two threads wont help, it will actually slow
down a bit things.

NAPI model already handles the 'one cpu, multiple queues/devices' quite
well.