From: John Fastabend <john.fastabend@gmail.com>
To: Brenden Blanco <bblanco@plumgrid.com>,
Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Tom Herbert <tom@herbertland.com>,
Daniel Borkmann <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
ogerlitz@mellanox.com
Subject: Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter
Date: Mon, 4 Apr 2016 09:07:03 -0700 [thread overview]
Message-ID: <57029127.3040303@gmail.com> (raw)
In-Reply-To: <20160404152948.GA495@gmail.com>
On 16-04-04 08:29 AM, Brenden Blanco wrote:
> On Mon, Apr 04, 2016 at 05:12:27PM +0200, Jesper Dangaard Brouer wrote:
>> On Mon, 4 Apr 2016 11:09:57 -0300
>> Tom Herbert <tom@herbertland.com> wrote:
>>
>>> On Mon, Apr 4, 2016 at 10:36 AM, Daniel Borkmann <daniel@iogearbox.net> wrote:
>>>> On 04/04/2016 03:07 PM, Jesper Dangaard Brouer wrote:
>>>>>
>>>>> On Mon, 04 Apr 2016 10:49:09 +0200 Daniel Borkmann <daniel@iogearbox.net>
>>>>> wrote:
>>>>>>
>>>>>> On 04/02/2016 03:21 AM, Brenden Blanco wrote:
>>>>>>>
>>>>>>> Add a new bpf prog type that is intended to run in early stages of the
>>>>>>> packet rx path. Only minimal packet metadata will be available, hence a
>>>>>>> new
>>>>>>> context type, struct xdp_metadata, is exposed to userspace. So far only
>>>>>>> expose the readable packet length, and only in read mode.
>>>>>>>
>>>>>>> The PHYS_DEV name is chosen to represent that the program is meant only
>>>>>>> for physical adapters, rather than all netdevs.
>>>>>>>
>>>>>>> While the user visible struct is new, the underlying context must be
>>>>>>> implemented as a minimal skb in order for the packet load_* instructions
>>>>>>> to work. The skb filled in by the driver must have skb->len, skb->head,
>>>>>>> and skb->data set, and skb->data_len == 0.
>>>>>>>
>>>>> [...]
>>>>>>
>>>>>>
>>>>>> Do you plan to support bpf_skb_load_bytes() as well? I like using
>>>>>> this API especially when dealing with larger chunks (>4 bytes) to
>>>>>> load into stack memory, plus content is kept in network byte order.
>>>>>>
>>>>>> What about other helpers such as bpf_skb_store_bytes() et al that
>>>>>> work on skbs. Do you intent to reuse them as is and thus populate
>>>>>> the per cpu skb with needed fields (faking linear data), or do you
>>>>>> see larger obstacles that prevent for this?
>>>>>
>>>>>
>>>>> Argh... maybe the minimal pseudo/fake SKB is the wrong "signal" to send
>>>>> to users of this API.
>>>>>
>>>>> The hole idea is that an SKB is NOT allocated yet, and not needed at
>>>>> this level. If we start supporting calling underlying SKB functions,
>>>>> then we will end-up in the same place (performance wise).
>>>>
>>>>
>>>> I'm talking about the current skb-related BPF helper functions we have,
>>>> so the question is how much from that code we have we can reuse under
>>>> these constraints (obviously things like the tunnel helpers are a different
>>>> story) and if that trade-off is acceptable for us. I'm also thinking
>>>> that, for example, if you need to parse the packet data anyway for a drop
>>>> verdict, you might as well pass some meta data (that is set in the real
>>>> skb later on) for those packets that go up the stack.
>>>
>>> Right, the meta data in this case is an abstracted receive descriptor.
>>> This would include items that we get in a device receive descriptor
>>> (computed checksum, hash, VLAN tag). This is purposely a small
>>> restricted data structure. I'm hoping we can minimize the size of this
>>> to not much more than 32 bytes (including pointers to data and
>>> linkage).
>>
>> I agree.
>>
>>> How this translates to skb to maintain compatibility is with BPF
>>> interesting question. One other consideration is that skb's are kernel
>>> specific, we should be able to use the same BPF filter program in
>>> userspace over DPDK for instance-- so an skb interface as the packet
>>> abstraction might not be the right model...
>>
>> I agree. I don't think reusing the SKB data structure is the right
>> model. We should drop the SKB pointer from the API.
>>
>> As Tom also points out, making the BPF interface independent of the SKB
>> meta-data structure, would also make the eBPF program more generally
>> applicable.
> The initial approach that I tried went down this path. Alexei advised
> that I use the pseudo skb, and in the future the API between drivers and
> bpf can change to adopt non-skb context. The only user facing ABIs in
> this patchset are the IFLA, the xdp_metadata struct, and the name of the
> new enum.
>
> The reason to use a pseudo skb for now is that there will be a fair
> amount of churn to get bpf jit and interpreter to understand non-skb
> context in the bpf_load_pointer() code. I don't see the need for
> requiring that for this patchset, as it will be internal-only change
> if/when we use something else.
Another option would be to have per driver JIT code to patch up the
skb read/loads with descriptor reads and metadata. From a strictly
performance stand point it should be better than pseudo skbs.
.John
next prev parent reply other threads:[~2016-04-04 16:07 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-02 1:21 [RFC PATCH 0/5] Add driver bpf hook for early packet drop Brenden Blanco
2016-04-02 1:21 ` [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter Brenden Blanco
2016-04-02 16:39 ` Tom Herbert
2016-04-03 7:02 ` Brenden Blanco
2016-04-04 22:07 ` Thomas Graf
2016-04-05 8:19 ` Jesper Dangaard Brouer
2016-04-04 8:49 ` Daniel Borkmann
2016-04-04 13:07 ` Jesper Dangaard Brouer
2016-04-04 13:36 ` Daniel Borkmann
2016-04-04 14:09 ` Tom Herbert
2016-04-04 15:12 ` Jesper Dangaard Brouer
2016-04-04 15:29 ` Brenden Blanco
2016-04-04 16:07 ` John Fastabend [this message]
2016-04-04 16:17 ` Brenden Blanco
2016-04-04 20:00 ` Alexei Starovoitov
2016-04-04 22:04 ` Thomas Graf
2016-04-05 2:25 ` Alexei Starovoitov
2016-04-05 8:11 ` Jesper Dangaard Brouer
2016-04-05 9:29 ` Jesper Dangaard Brouer
2016-04-05 22:06 ` Alexei Starovoitov
2016-04-04 14:33 ` Eric Dumazet
2016-04-04 15:18 ` Edward Cree
2016-04-02 1:21 ` [RFC PATCH 2/5] net: add ndo to set bpf prog in adapter rx Brenden Blanco
2016-04-02 1:21 ` [RFC PATCH 3/5] rtnl: add option for setting link bpf prog Brenden Blanco
2016-04-02 1:21 ` [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program Brenden Blanco
2016-04-02 2:08 ` Eric Dumazet
2016-04-02 2:47 ` Alexei Starovoitov
2016-04-04 14:57 ` Jesper Dangaard Brouer
2016-04-04 15:22 ` Eric Dumazet
2016-04-04 18:50 ` Alexei Starovoitov
2016-04-05 14:15 ` Or Gerlitz
2016-04-06 4:05 ` Brenden Blanco
2016-04-03 6:15 ` Brenden Blanco
2016-04-05 2:20 ` Brenden Blanco
2016-04-05 2:44 ` Eric Dumazet
2016-04-05 18:59 ` Eran Ben Elisha
2016-04-02 8:23 ` Jesper Dangaard Brouer
2016-04-03 6:11 ` Brenden Blanco
2016-04-04 18:27 ` Alexei Starovoitov
2016-04-05 6:04 ` Jesper Dangaard Brouer
2016-04-02 18:40 ` Johannes Berg
2016-04-03 6:38 ` Brenden Blanco
2016-04-04 7:35 ` Johannes Berg
2016-04-04 9:57 ` Daniel Borkmann
2016-04-04 18:46 ` Alexei Starovoitov
2016-04-04 21:01 ` Daniel Borkmann
2016-04-05 1:17 ` Alexei Starovoitov
2016-04-04 8:33 ` Jesper Dangaard Brouer
2016-04-04 9:22 ` Daniel Borkmann
2016-04-02 1:21 ` [RFC PATCH 5/5] Add sample for adding simple drop program to link Brenden Blanco
2016-04-06 19:48 ` Jesper Dangaard Brouer
2016-04-06 20:01 ` Jesper Dangaard Brouer
2016-04-06 23:11 ` Alexei Starovoitov
2016-04-06 20:03 ` Daniel Borkmann
2016-04-02 16:47 ` [RFC PATCH 0/5] Add driver bpf hook for early packet drop Tom Herbert
2016-04-03 5:41 ` Brenden Blanco
2016-04-04 7:48 ` Jesper Dangaard Brouer
2016-04-04 18:10 ` Alexei Starovoitov
2016-04-02 18:41 ` Johannes Berg
2016-04-02 22:57 ` Tom Herbert
2016-04-03 2:28 ` Lorenzo Colitti
2016-04-04 7:37 ` Johannes Berg
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