On Thu, 8 Apr 2021 14:50:53 +0200
Lorenzo Bianconi <lorenzo@xxxxxxxxxx> wrote:
> Introduce multi-buffer bit (mb) in xdp_frame/xdp_buffer data structure
> in order to specify if this is a linear buffer (mb = 0) or a multi-buffer
> frame (mb = 1). In the latter case the shared_info area at the end of the
> first buffer will be properly initialized to link together subsequent
> buffers.
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
> ---
> include/net/xdp.h | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index a5bc214a49d9..842580a61563 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -73,7 +73,10 @@ struct xdp_buff {
> void *data_hard_start;
> struct xdp_rxq_info *rxq;
> struct xdp_txq_info *txq;
> - u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
> + u32 frame_sz:31; /* frame size to deduce data_hard_end/reserved
> + * tailroom
> + */
> + u32 mb:1; /* xdp non-linear buffer */
> };
>
> static __always_inline void
> @@ -81,6 +84,7 @@ xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
> {
> xdp->frame_sz = frame_sz;
> xdp->rxq = rxq;
> + xdp->mb = 0;
> }
>
> static __always_inline void
> @@ -116,7 +120,8 @@ struct xdp_frame {
> u16 len;
> u16 headroom;
> u32 metasize:8;
> - u32 frame_sz:24;
> + u32 frame_sz:23;
> + u32 mb:1; /* xdp non-linear frame */
> /* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
> * while mem info is valid on remote CPU.
> */
So, it seems that these bitfield's are the root-cause of the
performance regression. Credit to Alexei whom wisely already point
this out[1] in V2 ;-)
[1] https://lore.kernel.org/netdev/20200904010705.jm6dnuyj3oq4cpjd@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> @@ -179,6 +184,7 @@ void xdp_convert_frame_to_buff(struct xdp_frame *frame, struct xdp_buff *xdp)
> xdp->data_end = frame->data + frame->len;
> xdp->data_meta = frame->data - frame->metasize;
> xdp->frame_sz = frame->frame_sz;
> + xdp->mb = frame->mb;
> }
>
> static inline
> @@ -205,6 +211,7 @@ int xdp_update_frame_from_buff(struct xdp_buff *xdp,
> xdp_frame->headroom = headroom - sizeof(*xdp_frame);
> xdp_frame->metasize = metasize;
> xdp_frame->frame_sz = xdp->frame_sz;
> + xdp_frame->mb = xdp->mb;
>
> return 0;
> }
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
