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SubjectRe: [PATCH net-next 0/3] support changing steering policies in tuntap
On Wed, Sep 27, 2017 at 04:23:54PM +0800, Jason Wang wrote:
> Hi all:
> We use flow caches based flow steering policy now. This is good for
> connection-oriented communication such as TCP but not for the others
> e.g connectionless unidirectional workload which cares only about
> pps. This calls the ability of supporting changing steering policies
> in tuntap which was done by this series.
> Flow steering policy was abstracted into tun_steering_ops in the first
> patch. Then new ioctls to set or query current policy were introduced,
> and the last patch introduces a very simple policy that select txq
> based on processor id as an example.
> Test was done by using xdp_redirect to redirect traffic generated from
> MoonGen that was running on a remote machine. And I see 37%
> improvement for processor id policy compared to automatic flow
> steering policy.

For sure, if you don't need to figure out the flow hash then you can
save a bunch of cycles. But I don't think the cpu policy is too
practical outside of a benchmark.

Did you generate packets and just send them to tun? If so, this is not a
typical configuration, is it? With packets coming e.g. from a real nic
they might already have the hash pre-calculated, and you won't
see the benefit.

> In the future, both simple and sophisticated policy like RSS or other guest
> driven steering policies could be done on top.

IMHO there should be a more practical example before adding all this
indirection. And it would be nice to understand why this queue selection
needs to be tun specific.

> Thanks
> Jason Wang (3):
> tun: abstract flow steering logic
> tun: introduce ioctls to set and get steering policies
> tun: introduce cpu id based steering policy
> drivers/net/tun.c | 151 +++++++++++++++++++++++++++++++++++++-------
> include/uapi/linux/if_tun.h | 8 +++
> 2 files changed, 136 insertions(+), 23 deletions(-)
> --
> 2.7.4

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