[Intel-wired-lan] [RFC PATCH bpf-next 05/12] xdp: add MEM_TYPE_ZERO_COPY

Björn Töpel bjorn.topel at gmail.com
Thu May 17 07:09:58 UTC 2018


2018-05-17 9:08 GMT+02:00 Björn Töpel <bjorn.topel at gmail.com>:
> 2018-05-17 7:57 GMT+02:00 Jesper Dangaard Brouer <brouer at redhat.com>:
>> On Tue, 15 May 2018 21:06:08 +0200
>> Björn Töpel <bjorn.topel at gmail.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


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