netdev - Re: [RFC PATCH v2 0/5] Add driver bpf hook for early packet drop

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Date:	Sat, 9 Apr 2016 10:37:51 -0400
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	Brenden Blanco <bblanco@...mgrid.com>, davem@...emloft.net
Cc:	netdev@...r.kernel.org, tom@...bertland.com,
	alexei.starovoitov@...il.com, ogerlitz@...lanox.com,
	daniel@...earbox.net, brouer@...hat.com, eric.dumazet@...il.com,
	ecree@...arflare.com, john.fastabend@...il.com, tgraf@...g.ch,
	johannes@...solutions.net, eranlinuxmellanox@...il.com,
	lorenzo@...gle.com
Subject: Re: [RFC PATCH v2 0/5] Add driver bpf hook for early packet drop

On 16-04-08 12:47 AM, Brenden Blanco wrote:
> This patch set introduces new infrastructure for programmatically
> processing packets in the earliest stages of rx, as part of an effort
> others are calling Express Data Path (XDP) [1]. Start this effort by
> introducing a new bpf program type for early packet filtering, before even
> an skb has been allocated.
>
> With this, hope to enable line rate filtering, with this initial
> implementation providing drop/allow action only.
>
> Patch 1 introduces the new prog type and helpers for validating the bpf
> program. A new userspace struct is defined containing only len as a field,
> with others to follow in the future.
> In patch 2, create a new ndo to pass the fd to support drivers.
> In patch 3, expose a new rtnl option to userspace.
> In patch 4, enable support in mlx4 driver. No skb allocation is required,
> instead a static percpu skb is kept in the driver and minimally initialized
> for each driver frag.
> In patch 5, create a sample drop and count program. With single core,
> achieved ~20 Mpps drop rate on a 40G mlx4. This includes packet data
> access, bpf array lookup, and increment.

Hrm. This doesnt sound very high (less than 50%?).
Is the driver the main overhead?
I'd be curious, for comparison, if you just dropped everything
without bpf and alternatively with tc + bpf of the same program
on the one cpu.
Numbers we had for the NUC with tc on single core were a bit higher
than 20Mpps but there was no driver overhead - so i expected
to see much higher numbers if you did it at the driver...
Note back in the day Alexey(not Alexei;->) had a built-in driver
level forwarder;
however the advantage there was derived out of packets being DMAed
from ingress to egress port after some simple lookup.

cheers,
jamal