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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Maciej Fijalkowski , Stanislav Fomichev , Magnus Karlsson , nex.sw.ncis.osdt.itp.upstreaming@intel.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v5 12/19] xdp: add generic xdp_build_skb_from_buff() Message-ID: References: <20241113152442.4000468-1-aleksander.lobakin@intel.com> <20241113152442.4000468-13-aleksander.lobakin@intel.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Nov 14, 2024 at 05:06:06PM +0200, Ido Schimmel wrote: > Looks good (no objections to the patch), but I have a question. See > below. > > On Wed, Nov 13, 2024 at 04:24:35PM +0100, Alexander Lobakin wrote: > > The code which builds an skb from an &xdp_buff keeps multiplying itself > > around the drivers with almost no changes. Let's try to stop that by > > adding a generic function. > > Unlike __xdp_build_skb_from_frame(), always allocate an skbuff head > > using napi_build_skb() and make use of the available xdp_rxq pointer to > > assign the Rx queue index. In case of PP-backed buffer, mark the skb to > > be recycled, as every PP user's been switched to recycle skbs. > > > > Reviewed-by: Toke Høiland-Jørgensen > > Signed-off-by: Alexander Lobakin > > Reviewed-by: Ido Schimmel > > > --- > > include/net/xdp.h | 1 + > > net/core/xdp.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 56 insertions(+) > > > > diff --git a/include/net/xdp.h b/include/net/xdp.h > > index 4c19042adf80..b0a25b7060ff 100644 > > --- a/include/net/xdp.h > > +++ b/include/net/xdp.h > > @@ -330,6 +330,7 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags, > > void xdp_warn(const char *msg, const char *func, const int line); > > #define XDP_WARN(msg) xdp_warn(msg, __func__, __LINE__) > > > > +struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp); > > struct xdp_frame *xdp_convert_zc_to_xdp_frame(struct xdp_buff *xdp); > > struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf, > > struct sk_buff *skb, > > diff --git a/net/core/xdp.c b/net/core/xdp.c > > index b1b426a9b146..3a9a3c14b080 100644 > > --- a/net/core/xdp.c > > +++ b/net/core/xdp.c > > @@ -624,6 +624,61 @@ int xdp_alloc_skb_bulk(void **skbs, int n_skb, gfp_t gfp) > > } > > EXPORT_SYMBOL_GPL(xdp_alloc_skb_bulk); > > > > +/** > > + * xdp_build_skb_from_buff - create an skb from an &xdp_buff > > + * @xdp: &xdp_buff to convert to an skb > > + * > > + * Perform common operations to create a new skb to pass up the stack from > > + * an &xdp_buff: allocate an skb head from the NAPI percpu cache, initialize > > + * skb data pointers and offsets, set the recycle bit if the buff is PP-backed, > > + * Rx queue index, protocol and update frags info. > > + * > > + * Return: new &sk_buff on success, %NULL on error. > > + */ > > +struct sk_buff *xdp_build_skb_from_buff(const struct xdp_buff *xdp) > > +{ > > + const struct xdp_rxq_info *rxq = xdp->rxq; > > + const struct skb_shared_info *sinfo; > > + struct sk_buff *skb; > > + u32 nr_frags = 0; > > + int metalen; > > + > > + if (unlikely(xdp_buff_has_frags(xdp))) { > > + sinfo = xdp_get_shared_info_from_buff(xdp); > > + nr_frags = sinfo->nr_frags; > > + } > > + > > + skb = napi_build_skb(xdp->data_hard_start, xdp->frame_sz); > > + if (unlikely(!skb)) > > + return NULL; > > + > > + skb_reserve(skb, xdp->data - xdp->data_hard_start); > > + __skb_put(skb, xdp->data_end - xdp->data); > > + > > + metalen = xdp->data - xdp->data_meta; > > + if (metalen > 0) > > + skb_metadata_set(skb, metalen); > > + > > + if (is_page_pool_compiled_in() && rxq->mem.type == MEM_TYPE_PAGE_POOL) > > + skb_mark_for_recycle(skb); > > + > > + skb_record_rx_queue(skb, rxq->queue_index); > > + > > + if (unlikely(nr_frags)) { > > + u32 tsize; > > + > > + tsize = sinfo->xdp_frags_truesize ? : nr_frags * xdp->frame_sz; > > + xdp_update_skb_shared_info(skb, nr_frags, > > + sinfo->xdp_frags_size, tsize, > > + xdp_buff_is_frag_pfmemalloc(xdp)); > > + } > > + > > + skb->protocol = eth_type_trans(skb, rxq->dev); > > The device we are working with has more ports (net devices) than Rx > queues, so each queue can receive packets from different net devices. > Currently, each Rx queue has its own NAPI instance and its own page > pool. All the Rx NAPI instances are initialized using the same dummy net > device which is allocated using alloc_netdev_dummy(). > > What are our options with regards to the XDP Rx queue info structure? As > evident by this patch, it does not seem valid to register one such > structure per Rx queue and pass the dummy net device. Would it be valid > to register one such structure per port (net device) and pass zero for > the queue index and NAPI ID? Actually, this does not seem to be valid either as we need to associate an XDP Rx queue info with the correct page pool :/ > > To be clear, I understand it is not a common use case. > > Thanks > > > + > > + return skb; > > +} > > +EXPORT_SYMBOL_GPL(xdp_build_skb_from_buff); > > + > > struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf, > > struct sk_buff *skb, > > struct net_device *dev) > > -- > > 2.47.0 > > > >