netdev - Re: [RFC PATCH bpf-next 05/12] xdp: add MEM_TYPE_ZERO

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Date:   Thu, 17 May 2018 09:09:58 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Netdev <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [RFC PATCH bpf-next 05/12] xdp: add MEM_TYPE_ZERO_COPY

2018-05-17 9:08 GMT+02:00 Björn Töpel <bjorn.topel@...il.com>:
> 2018-05-17 7:57 GMT+02:00 Jesper Dangaard Brouer <brouer@...hat.com>:
>> On Tue, 15 May 2018 21:06:08 +0200
>> Björn Töpel <bjorn.topel@...il.com> wrote:
>>
>>> @@ -82,6 +88,10 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
>>>       int metasize;
>>>       int headroom;
>>>
>>> +     // XXX implement clone, copy, use "native" MEM_TYPE
>>> +     if (xdp->rxq->mem.type == MEM_TYPE_ZERO_COPY)
>>> +             return NULL;
>>> +
>>
>> There is going to be significant tradeoffs between AF_XDP zero-copy and
>> copy-variant.  The copy-variant, still have very attractive
>> RX-performance, and other benefits like no exposing unrelated packets
>> to userspace (but limit these to the XDP filter).
>>
>> Thus, as a user I would like to choose between AF_XDP zero-copy and
>> copy-variant. Even if my NIC support zero-copy, I can be interested in
>> only enabling the copy-variant. This patchset doesn't let me choose.
>>
>> How do we expose this to userspace?
>> (Maybe as simple as an sockaddr_xdp->sxdp_flags flag?)
>>
>
> We planned to add these flags later, but I think you're right that
> it's better to do that right away.
>
> If we try to follow the behavior of the XDP netlink interface: Pick
> the "the best mode" when there are no flags. A user would like to
> "force" a mode -- meaning that you select, say copy, and getting an
> error if that's not supported. Four new flags?
>
> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> index 77b88c4efe98..ce1f710847b7 100644
> --- a/include/uapi/linux/if_xdp.h
> +++ b/include/uapi/linux/if_xdp.h
> @@ -22,7 +22,11 @@
>  #include <linux/types.h>
>
>  /* Options for the sxdp_flags field */
> -#define XDP_SHARED_UMEM 1
> +#define XDP_SHARED_UMEM        (1U << 0)
> +#define XDP_COPY_TX_UMEM    (1U << 1)
> +#define XDP_ZEROCOPY_TX_UMEM    (1U << 2)
> +#define XDP_COPY_RX_UMEM    (1U << 3)
> +#define XDP_ZEROCOPY_RX_UMEM    (1U << 4)
>
>  struct sockaddr_xdp {
>      __u16 sxdp_family;
>
> A better way?
>

...but without the _UMEM suffix obviously.

>
>
>
>> --
>> Best regards,
>>   Jesper Dangaard Brouer
>>   MSc.CS, Principal Kernel Engineer at Red Hat
>>   LinkedIn: http://www.linkedin.com/in/brouer