netdev - Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter

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Date:	Mon, 4 Apr 2016 19:25:08 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Brenden Blanco <bblanco@...mgrid.com>,
	John Fastabend <john.fastabend@...il.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Tom Herbert <tom@...bertland.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	ogerlitz@...lanox.com
Subject: Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver
 filter

On Tue, Apr 05, 2016 at 12:04:39AM +0200, Thomas Graf wrote:
> On 04/04/16 at 01:00pm, Alexei Starovoitov wrote:
> > Exactly. That the most important part of this rfc.
> > Right now redirect to different queue, batching, prefetch and tons of
> > other code are mising. We have to plan the whole project, so we can
> > incrementally add features without breaking abi.
> > So new IFLA, xdp_metadata struct and enum for bpf return codes are
> > the main things to agree on.
> 
> +1
> This is the most important statement in this thread so far. A plan
> that gets us from this RFC series to a functional forwarding engine
> with redirect and load/write is essential. [...]

exactly. I think the next step 2 is to figure out the redirect return code
and 'rewiring' of the rx dma buffer into tx ring and auto-batching.
As this rfc showed even when using standard page alloc/free the peformance
is hitting 10Gbps hw limit and not being cpu bounded, so recycling of
the pages and avoiding map/unmap will come at step 3.
Batching is necessary even for basic redirect, since ringing doorbell
for every tx buffer is not an option.

> [...] I would really like to see a common set of helpers which
> applies to both cls_bpf and phys_dev. Given the existing skb based
> helpers cannot be overloaded, at least the phys_dev helpers should
> be made to work in cls_bpf context as well to allow for some
> portability. Otherwise we'll end up with half a dozen flavours of
> BPF which are all incompatible.

The helpers can be 'overloaded'. In my upcoming patches for
bpf+tracepoints the bpf_perf_event_output() helper is different
depending on program type (kprobe vs tracepoint), but logically
it looks exactly the same from program point of view and
BPF_FUNC_id is reused.
So for cls_bpf vs bpf_phys_dev we can have the same bpf_csum_diff()
helper which will have different internal implementation depending
on program type.