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.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 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);
+
+	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

Alexander Lobakin <aleksander.lobakin@intel.com> writes:

> 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.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>

Alexander Lobakin <aleksander.lobakin@intel.com> writes:

> 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.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> ---
>  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;
> +	}

Why this separate branch at the start of the function? nr_frags is no
used until the other branch below, so why not just make that branch on
xdp_buff_has_frags() and keep everything frags-related together in one
block?

-Toke

From: Toke Høiland-Jørgensen <toke@redhat.com>
Date: Mon, 11 Nov 2024 17:39:51 +0100

> Alexander Lobakin <aleksander.lobakin@intel.com> writes:
> 
>> 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.
>>
>> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
>> ---
>>  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;
>> +	}
> 
> Why this separate branch at the start of the function? nr_frags is no
> used until the other branch below, so why not just make that branch on
> xdp_buff_has_frags() and keep everything frags-related together in one
> block?

Because napi_build_skb() will call build_skb_around() which will
memset() a piece of shared info including nr_frags.
xdp_build_skb_from_frame() has the same logic. I'd be happy to have only
one block, but I can't =\

> 
> -Toke

Thanks,
Olek

Alexander Lobakin <aleksander.lobakin@intel.com> writes:

> From: Toke Høiland-Jørgensen <toke@redhat.com>
> Date: Mon, 11 Nov 2024 17:39:51 +0100
>
>> Alexander Lobakin <aleksander.lobakin@intel.com> writes:
>> 
>>> 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.
>>>
>>> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
>>> ---
>>>  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;
>>> +	}
>> 
>> Why this separate branch at the start of the function? nr_frags is no
>> used until the other branch below, so why not just make that branch on
>> xdp_buff_has_frags() and keep everything frags-related together in one
>> block?
>
> Because napi_build_skb() will call build_skb_around() which will
> memset() a piece of shared info including nr_frags.
> xdp_build_skb_from_frame() has the same logic. I'd be happy to have only
> one block, but I can't =\

Ah, right. Annoying, but OK :)

-Toke