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Date: Tue, 7 Sep 2021 16:46:23 +0200
From: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To: Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
netdev@...r.kernel.org, brouer@...hat.com, davem@...emloft.net,
kuba@...nel.org, ast@...nel.org, daniel@...earbox.net,
shayagr@...zon.com, john.fastabend@...il.com, dsahern@...nel.org,
echaudro@...hat.com, jasowang@...hat.com,
alexander.duyck@...il.com, saeed@...nel.org,
maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
tirthendu.sarkar@...el.com, toke@...hat.com
Subject: Re: [PATCH v13 bpf-next 02/18] xdp: introduce flags field in
xdp_buff/xdp_frame
> (Minor changes requested below)
>
> On 07/09/2021 14.35, Lorenzo Bianconi wrote:
> > Introduce flags field in xdp_frame and xdp_buffer data structures
> > to define additional buffer features. At the moment the only
> > supported buffer feature is multi-buffer bit (mb). Multi-buffer bit
> > is used to specify if this is a linear buffer (mb = 0) or a multi-buffer
> > frame (mb = 1). In the latter case the driver is expected to initialize
> > the skb_shared_info structure at the end of the first buffer to link
> > together subsequent buffers belonging to the same frame.
> >
> > Acked-by: John Fastabend <john.fastabend@...il.com>
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> > include/net/xdp.h | 29 +++++++++++++++++++++++++++++
> > 1 file changed, 29 insertions(+)
> >
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index ad5b02dcb6f4..ed5ea784fd45 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -66,6 +66,10 @@ struct xdp_txq_info {
> > struct net_device *dev;
> > };
> > +enum xdp_buff_flags {
> > + XDP_FLAGS_MULTI_BUFF = BIT(0), /* non-linear xdp buff */
> > +};
> > +
> > struct xdp_buff {
> > void *data;
> > void *data_end;
> > @@ -74,13 +78,30 @@ struct xdp_buff {
> > struct xdp_rxq_info *rxq;
> > struct xdp_txq_info *txq;
> > u32 frame_sz; /* frame size to deduce data_hard_end/reserved tailroom*/
> > + u16 flags; /* supported values defined in xdp_flags */
> ^^^^^^^^^
> Variable/enum is named "xdp_buff_flags", but comment says "xdp_flags".
ack, I will fix it in v14
>
> I think we should change flags to use u32, because xdp_buff already contain
> 4 byte padding. (pahole output provided as help below)
ack, I will fix it in v14
>
> > };
> > +static __always_inline bool xdp_buff_is_mb(struct xdp_buff *xdp)
> > +{
> > + return !!(xdp->flags & XDP_FLAGS_MULTI_BUFF);
> > +}
> > +
> > +static __always_inline void xdp_buff_set_mb(struct xdp_buff *xdp)
> > +{
> > + xdp->flags |= XDP_FLAGS_MULTI_BUFF;
> > +}
> > +
> > +static __always_inline void xdp_buff_clear_mb(struct xdp_buff *xdp)
> > +{
> > + xdp->flags &= ~XDP_FLAGS_MULTI_BUFF;
> > +}
> > +
> > static __always_inline void
> > xdp_init_buff(struct xdp_buff *xdp, u32 frame_sz, struct xdp_rxq_info *rxq)
> > {
> > xdp->frame_sz = frame_sz;
> > xdp->rxq = rxq;
> > + xdp->flags = 0;
> > }
> > static __always_inline void
> > @@ -122,8 +143,14 @@ struct xdp_frame {
> > */
> > struct xdp_mem_info mem;
> > struct net_device *dev_rx; /* used by cpumap */
> > + u16 flags; /* supported values defined in xdp_flags */
> ^^^^^^^^^
> Variable/enum is named "xdp_buff_flags", but comment says "xdp_flags".
>
> Here (for xdp_frame) I also think we should change flags to u32, because
> adding this u16 cause extra padding anyhow. (pahole output provided as help
> below).
ack, I will fix it in v14
>
>
> > };
> > +static __always_inline bool xdp_frame_is_mb(struct xdp_frame *frame)
> > +{
> > + return !!(frame->flags & XDP_FLAGS_MULTI_BUFF);
> > +}
> > +
> > #define XDP_BULK_QUEUE_SIZE 16
> > struct xdp_frame_bulk {
> > int count;
> > @@ -180,6 +207,7 @@ 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->flags = frame->flags;
> > }
> > static inline
> > @@ -206,6 +234,7 @@ 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->flags = xdp->flags;
> > return 0;
> > }
> >
>
>
>
> Details below... no need to read any further
>
> Investigating struct xdp_frame with pahole:
>
> $ pahole -C xdp_frame net/core/xdp.o
> struct xdp_frame {
> void * data; /* 0 8 */
> u16 len; /* 8 2 */
> u16 headroom; /* 10 2 */
> u32 metasize:8; /* 12: 0 4 */
> u32 frame_sz:24; /* 12: 8 4 */
> struct xdp_mem_info mem; /* 16 8 */
> struct net_device * dev_rx; /* 24 8 */
>
> /* size: 32, cachelines: 1, members: 7 */
> /* last cacheline: 32 bytes */
> };
>
>
> pahole -C xdp_frame net/core/xdp.o
> struct xdp_frame {
> void * data; /* 0 8 */
> u16 len; /* 8 2 */
> u16 headroom; /* 10 2 */
> u32 metasize:8; /* 12: 0 4 */
> u32 frame_sz:24; /* 12: 8 4 */
> struct xdp_mem_info mem; /* 16 8 */
> struct net_device * dev_rx; /* 24 8 */
> u16 flags; /* 32 2 */
>
> /* size: 40, cachelines: 1, members: 8 */
> /* padding: 6 */
> /* last cacheline: 40 bytes */
> };
>
>
> $ pahole -C xdp_frame net/core/xdp.o
> struct xdp_frame {
> void * data; /* 0 8 */
> u16 len; /* 8 2 */
> u16 headroom; /* 10 2 */
> u32 metasize:8; /* 12: 0 4 */
> u32 frame_sz:24; /* 12: 8 4 */
> struct xdp_mem_info mem; /* 16 8 */
> struct net_device * dev_rx; /* 24 8 */
> u32 flags; /* 32 4 */
>
> /* size: 40, cachelines: 1, members: 8 */
> /* padding: 4 */
> /* last cacheline: 40 bytes */
> };
>
>
> Details for struct xdp_buff, it already contains 4 bytes padding.
>
> $ pahole -C xdp_buff net/core/xdp.o
> struct xdp_buff {
> void * data; /* 0 8 */
> void * data_end; /* 8 8 */
> void * data_meta; /* 16 8 */
> void * data_hard_start; /* 24 8 */
> struct xdp_rxq_info * rxq; /* 32 8 */
> struct xdp_txq_info * txq; /* 40 8 */
> u32 frame_sz; /* 48 4 */
> u16 flags; /* 52 2 */
>
> /* size: 56, cachelines: 1, members: 8 */
> /* padding: 2 */
> /* last cacheline: 56 bytes */
> };
ack, right.
Regards,
Lorenzo
>
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