[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <B51B5C91-D388-4BF4-97B2-0A4AF5B365A4@intel.com>
Date: Thu, 19 Nov 2020 00:57:17 +0000
From: "Patel, Vedang" <vedang.patel@...el.com>
To: Saeed Mahameed <saeed@...nel.org>
CC: Jesper Dangaard Brouer <jbrouer@...hat.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"Gomes, Vinicius" <vinicius.gomes@...el.com>,
"Guedes, Andre" <andre.guedes@...el.com>
Subject: Re: Hardware time stamping support for AF_XDP applications
Hi Saeed,
> On Nov 13, 2020, at 10:02 AM, Patel, Vedang <vedang.patel@...el.com> wrote:
>
> Hi Saeed,
>
>> On Nov 12, 2020, at 11:31 AM, Saeed Mahameed <saeed@...nel.org> wrote:
>>
>> On Tue, 2020-11-10 at 23:53 +0000, Patel, Vedang wrote:
>>>> With BTF formatted metadata it is up to the driver to advertise
>>>> whatever it can/want :)
>>>> so yes.
>>>
>>> I have a very basic question here. From what I understand about BTF,
>>> I can generate a header file (using bpftool?) containing the BTF data
>>> format provided by the driver. If so, how can I design an application
>>> which can work with multiple NICs drivers without recompilation? I am
>>> guessing there is some sort of “master list” of HW hints the drivers
>>> will agree upon?
>>
>> Hi Patel, as Jesper mentioned, some hints will be well defined in BTF
>> format, by name, size and type, e.g.:
>>
>> u32 hash32;
>> u16 vlan_tci;
>> u64 timestamp;
>>
>> etc..
>>
>> if the driver reports only well known hints, a program compiled with
>> these can work in theory on any NIC that supports them. the BPF program
>> loader/verifier in the kernel can check compatibility before loading a
>> program on a NIC.
>>
>> now the question remains, What if different NICs/Drivers re-arrange
>> those fields differently?
>> this also can be solved by the BPF XDP program loader in the kernel at
>> rung time, it can re-arrange the meta data offsets according to the
>> current NIC directly in the byte code, but this is going to be a future
>> work.
>>
> Thanks for more info!
>
> I have pulled in your changes and started modifying the igc driver. I will report back on how it goes.
>
I was able to add support for igc and now I have a few more opens about the feature:
- i225 contains multiple PHC clocks which can report timestamps for a packet. So, along with the timestamp, we also need to return clock id which was used to timestamp the packet. I was wondering if there are other NICs which have similar functionalities so that we can align on the interface used to present the timestamp to AF_XDP sockets.
- I am also planning to add capability to set timestamp using AF_XDP socket. I am just planning to add another socket option (like what is done in AF_PACKET). Let me know if there are other ideas.
- From what I understand metadata size will be accounted for in the XDP_PACKET_HEADROOM. Is that correct? If so, what will happen in the scenario when the metadata exceeds the amount of space available (XDP_PACKET_HEADROOM - sizeof(struct xdp_frame))?
- From looking at the code, it looks like BTF metadata will be enabled at NIC level. So, all AF_XDP sockets will receive metadata whether they want it or not. Do we need a knob for AF_XDP sockets to enable metadata? I think applications which expect larger frame size will not want metadata in order to save space.
Thanks,
Vedang
> Thanks,
> Vedang
Powered by blists - more mailing lists