netdev - Re: [net-next sample action optimization v4 3/4] openvswitch: Optimize sample action for the clone use cases

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Date:   Tue, 21 Mar 2017 22:59:46 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Andy Zhou <azhou@....org>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Joe Stringer <joe@....org>
Subject: Re: [net-next sample action optimization v4 3/4] openvswitch:
 Optimize sample action for the clone use cases

On Mon, Mar 20, 2017 at 4:32 PM, Andy Zhou <azhou@....org> wrote:
> With the introduction of open flow 'clone' action, the OVS user space
> can now translate the 'clone' action into kernel datapath 'sample'
> action, with 100% probability, to ensure that the clone semantics,
> which is that the packet seen by the clone action is the same as the
> packet seen by the action after clone, is faithfully carried out
> in the datapath.
>
> While the sample action in the datpath has the matching semantics,
> its implementation is only optimized for its original use.
> Specifically, there are two limitation: First, there is a 3 level of
> nesting restriction, enforced at the flow downloading time. This
> limit turns out to be too restrictive for the 'clone' use case.
> Second, the implementation avoid recursive call only if the sample
> action list has a single userspace action.
>
> The main optimization implemented in this series removes the static
> nesting limit check, instead, implement the run time recursion limit
> check, and recursion avoidance similar to that of the 'recirc' action.
> This optimization solve both #1 and #2 issues above.
>
> One related optimization attempts to avoid copying flow key as
> long as the actions enclosed does not change the flow key. The
> detection is performed only once at the flow downloading time.
>
> Another related optimization is to rewrite the action list
> at flow downloading time in order to save the fast path from parsing
> the sample action list in its original form repeatedly.
>
> Signed-off-by: Andy Zhou <azhou@....org>

Acked-by: Pravin B Shelar <pshelar@....org>