[PATCH net-next 0/6] sk_buff: optimize GRO for the common case

[PATCH net-next 0/6] sk_buff: optimize GRO for the common case

[Paolo Abeni]

This is a trimmed down revision of "sk_buff: optimize layout for GRO",
specifically dropping the changes to the sk_buff layout[1].

This series tries to accomplish 2 goals:
- optimize the GRO stage for the most common scenario, avoiding a bunch
  of conditional and some more code
- let owned skbs entering the GRO engine, allowing backpressure in the
  veth GRO forward path.

A new sk_buff flag (!!!) is introduced and maintained for GRO's sake.
Such field uses an existing hole, so there is no change to the sk_buff
size.

[1] two main reasons:
- move skb->inner_ field requires some extra care, as some in kernel
  users access and the fields regardless of skb->encapsulation.
- extending secmark size clash with ct and nft uAPIs

address the all above is possible, I think, but for sure not in a single
series.

Paolo Abeni (6):
  sk_buff: introduce 'slow_gro' flags
  sk_buff: track dst status in slow_gro
  sk_buff: track extension status in slow_gro
  net: optimize GRO for the common case.
  skbuff: allow 'slow_gro' for skb carring sock reference
  veth: use skb_prepare_for_gro()

 drivers/net/veth.c     |  2 +-
 include/linux/skbuff.h |  6 ++++++
 include/net/dst.h      |  2 ++
 include/net/sock.h     |  9 +++++++++
 net/core/dev.c         | 32 ++++++++++++++++++++++++--------
 net/core/skbuff.c      | 27 ++++++++++++++++++++-------
 6 files changed, 62 insertions(+), 16 deletions(-)

-- 
2.26.3

[PATCH net-next 1/6] sk_buff: introduce 'slow_gro' flags

[Paolo Abeni]

The new flag tracks if any state field is set, so that
GRO requires 'unusual'/slow prepare steps.

Set such flag when a ct entry is attached to the skb,
and never clear it.

The new bit uses an existing hole into the sk_buff struct

RFC -> v1:
 - use a single state bit, never clear it
 - avoid moving the _nfct field

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/skbuff.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f19190820e63..3ff18300d210 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -689,6 +689,7 @@ typedef unsigned char *sk_buff_data_t;
  *		CHECKSUM_UNNECESSARY (max 3)
  *	@dst_pending_confirm: need to confirm neighbour
  *	@decrypted: Decrypted SKB
+ *	@slow_gro: state present at GRO time, slower prepare step required
  *	@napi_id: id of the NAPI struct this skb came from
  *	@sender_cpu: (aka @napi_id) source CPU in XPS
  *	@secmark: security marking
@@ -870,6 +871,7 @@ struct sk_buff {
 #ifdef CONFIG_TLS_DEVICE
 	__u8			decrypted:1;
 #endif
+	__u8			slow_gro:1;
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */
@@ -4216,6 +4218,7 @@ static inline unsigned long skb_get_nfct(const struct sk_buff *skb)
 static inline void skb_set_nfct(struct sk_buff *skb, unsigned long nfct)
 {
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
+	skb->slow_gro |= !!nfct;
 	skb->_nfct = nfct;
 #endif
 }
@@ -4375,6 +4378,7 @@ static inline void nf_copy(struct sk_buff *dst, const struct sk_buff *src)
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
 	nf_conntrack_put(skb_nfct(dst));
 #endif
+	dst->slow_gro = src->slow_gro;
 	__nf_copy(dst, src, true);
 }
 
-- 
2.26.3

[PATCH net-next 2/6] sk_buff: track dst status in slow_gro

[Paolo Abeni]

Similar to the previous patch, but covering the dst field:
the slow_gro flag is additionally set when a dst is attached
to the skb

RFC -> v1:
 - use the existing flag instead of adding a new one

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/linux/skbuff.h | 2 ++
 include/net/dst.h      | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3ff18300d210..b1e5bbfcc926 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -992,6 +992,7 @@ static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
  */
 static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
 {
+	skb->slow_gro |= !!dst;
 	skb->_skb_refdst = (unsigned long)dst;
 }
 
@@ -1008,6 +1009,7 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
 static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
 {
 	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
+	skb->slow_gro = !!dst;
 	skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
 }
 
diff --git a/include/net/dst.h b/include/net/dst.h
index 75b1e734e9c2..a057319aabef 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -277,6 +277,7 @@ static inline void skb_dst_drop(struct sk_buff *skb)
 
 static inline void __skb_dst_copy(struct sk_buff *nskb, unsigned long refdst)
 {
+	nskb->slow_gro |= !!refdst;
 	nskb->_skb_refdst = refdst;
 	if (!(nskb->_skb_refdst & SKB_DST_NOREF))
 		dst_clone(skb_dst(nskb));
@@ -316,6 +317,7 @@ static inline bool skb_dst_force(struct sk_buff *skb)
 			dst = NULL;
 
 		skb->_skb_refdst = (unsigned long)dst;
+		skb->slow_gro |= !!dst;
 	}
 
 	return skb->_skb_refdst != 0UL;
-- 
2.26.3

Re: [PATCH net-next 2/6] sk_buff: track dst status in slow_gro

[Jakub Kicinski]

On Wed, 28 Jul 2021 18:24:00 +0200 Paolo Abeni wrote:
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 3ff18300d210..b1e5bbfcc926 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -992,6 +992,7 @@ static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
>   */
>  static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
>  {
> +	skb->slow_gro |= !!dst;
>  	skb->_skb_refdst = (unsigned long)dst;
>  }
>  
> @@ -1008,6 +1009,7 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
>  static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
>  {
>  	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
> +	skb->slow_gro = !!dst;

why is this one = and not |= ?

>  	skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
>  }

Re: [PATCH net-next 2/6] sk_buff: track dst status in slow_gro

[Paolo Abeni]

On Fri, 2021-07-30 at 04:08 -0700, Jakub Kicinski wrote:
> On Wed, 28 Jul 2021 18:24:00 +0200 Paolo Abeni wrote:
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 3ff18300d210..b1e5bbfcc926 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -992,6 +992,7 @@ static inline struct dst_entry *skb_dst(const struct sk_buff *skb)
> >   */
> >  static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
> >  {
> > +	skb->slow_gro |= !!dst;
> >  	skb->_skb_refdst = (unsigned long)dst;
> >  }
> >  
> > @@ -1008,6 +1009,7 @@ static inline void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)
> >  static inline void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
> >  {
> >  	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
> > +	skb->slow_gro = !!dst;
> 
> why is this one = and not |= ?

Mostly because I'm dumb. Sabrina Dubroca noted that already. I'll send
a follow-up ASAP.

Thanks!

Paolo

[PATCH net-next 3/6] sk_buff: track extension status in slow_gro

[Paolo Abeni]

Similar to the previous one, but tracking the
active_extensions field status.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/core/skbuff.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 517ee2c36425..a990e11c393c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6455,6 +6455,7 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
 	new->chunks = newlen;
 	new->offset[id] = newoff;
 set_active:
+	skb->slow_gro = 1;
 	skb->extensions = new;
 	skb->active_extensions |= 1 << id;
 	return skb_ext_get_ptr(new, id);
-- 
2.26.3

[PATCH net-next 4/6] net: optimize GRO for the common case.

[Paolo Abeni]

After the previous patches, at GRO time, skb->slow_gro is
usually 0, unless the packets comes from some H/W offload
slowpath or tunnel.

We can optimize the GRO code assuming !skb->slow_gro is likely.
This remove multiple conditionals in the most common path, at the
price of an additional one when we hit the above "slow-paths".

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/core/dev.c    | 30 ++++++++++++++++++++++--------
 net/core/skbuff.c |  9 ++++++---
 2 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fb5d12a3d52d..19565f7497ee 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6014,7 +6014,6 @@ static void gro_list_prepare(const struct list_head *head,
 		diffs |= skb_vlan_tag_present(p) ^ skb_vlan_tag_present(skb);
 		if (skb_vlan_tag_present(p))
 			diffs |= skb_vlan_tag_get(p) ^ skb_vlan_tag_get(skb);
-		diffs |= skb_metadata_dst_cmp(p, skb);
 		diffs |= skb_metadata_differs(p, skb);
 		if (maclen == ETH_HLEN)
 			diffs |= compare_ether_header(skb_mac_header(p),
@@ -6024,17 +6023,29 @@ static void gro_list_prepare(const struct list_head *head,
 				       skb_mac_header(skb),
 				       maclen);
 
-		diffs |= skb_get_nfct(p) ^ skb_get_nfct(skb);
+		/* in most common scenarions _state is 0
+		 * otherwise we are already on some slower paths
+		 * either skip all the infrequent tests altogether or
+		 * avoid trying too hard to skip each of them individually
+		 */
+		if (!diffs && unlikely(skb->slow_gro | p->slow_gro)) {
+#if IS_ENABLED(CONFIG_SKB_EXTENSIONS) && IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
+			struct tc_skb_ext *skb_ext;
+			struct tc_skb_ext *p_ext;
+#endif
+
+			diffs |= skb_metadata_dst_cmp(p, skb);
+			diffs |= skb_get_nfct(p) ^ skb_get_nfct(skb);
+
 #if IS_ENABLED(CONFIG_SKB_EXTENSIONS) && IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
-		if (!diffs) {
-			struct tc_skb_ext *skb_ext = skb_ext_find(skb, TC_SKB_EXT);
-			struct tc_skb_ext *p_ext = skb_ext_find(p, TC_SKB_EXT);
+			skb_ext = skb_ext_find(skb, TC_SKB_EXT);
+			p_ext = skb_ext_find(p, TC_SKB_EXT);
 
 			diffs |= (!!p_ext) ^ (!!skb_ext);
 			if (!diffs && unlikely(skb_ext))
 				diffs |= p_ext->chain ^ skb_ext->chain;
-		}
 #endif
+		}
 
 		NAPI_GRO_CB(p)->same_flow = !diffs;
 	}
@@ -6299,8 +6310,11 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 	skb->encapsulation = 0;
 	skb_shinfo(skb)->gso_type = 0;
 	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
-	skb_ext_reset(skb);
-	nf_reset_ct(skb);
+	if (unlikely(skb->slow_gro)) {
+		skb_ext_reset(skb);
+		nf_reset_ct(skb);
+		skb->slow_gro = 0;
+	}
 
 	napi->skb = skb;
 }
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a990e11c393c..8231cbddb6ed 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -954,9 +954,12 @@ void __kfree_skb_defer(struct sk_buff *skb)
 
 void napi_skb_free_stolen_head(struct sk_buff *skb)
 {
-	nf_reset_ct(skb);
-	skb_dst_drop(skb);
-	skb_ext_put(skb);
+	if (unlikely(skb->slow_gro)) {
+		nf_reset_ct(skb);
+		skb_dst_drop(skb);
+		skb_ext_put(skb);
+		skb->slow_gro = 0;
+	}
 	napi_skb_cache_put(skb);
 }
 
-- 
2.26.3

[PATCH net-next 5/6] skbuff: allow 'slow_gro' for skb carring sock reference

[Paolo Abeni]

This change leverages the infrastructure introduced by the previous
patches to allow soft devices passing to the GRO engine owned skbs
without impacting the fast-path.

It's up to the GRO caller ensuring the slow_gro bit validity before
invoking the GRO engine. The new helper skb_prepare_for_gro() is
introduced for that goal.

On slow_gro, skbs are aggregated only with equal sk.
Additionally, skb truesize on GRO recycle and free is correctly
updated so that sk wmem is not changed by the GRO processing.

rfc-> v1:
 - fixed bad truesize on dev_gro_receive NAPI_FREE
 - use the existing state bit

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 include/net/sock.h |  9 +++++++++
 net/core/dev.c     |  2 ++
 net/core/skbuff.c  | 17 +++++++++++++----
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index f23cb259b0e2..ff1be7e7e90b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2249,6 +2249,15 @@ static inline __must_check bool skb_set_owner_sk_safe(struct sk_buff *skb, struc
 	return false;
 }
 
+static inline void skb_prepare_for_gro(struct sk_buff *skb)
+{
+	if (skb->destructor != sock_wfree) {
+		skb_orphan(skb);
+		return;
+	}
+	skb->slow_gro = 1;
+}
+
 void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 		    unsigned long expires);
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 19565f7497ee..dcc87fcd64ba 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6034,6 +6034,7 @@ static void gro_list_prepare(const struct list_head *head,
 			struct tc_skb_ext *p_ext;
 #endif
 
+			diffs |= p->sk != skb->sk;
 			diffs |= skb_metadata_dst_cmp(p, skb);
 			diffs |= skb_get_nfct(p) ^ skb_get_nfct(skb);
 
@@ -6311,6 +6312,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 	skb_shinfo(skb)->gso_type = 0;
 	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
 	if (unlikely(skb->slow_gro)) {
+		skb_orphan(skb);
 		skb_ext_reset(skb);
 		nf_reset_ct(skb);
 		skb->slow_gro = 0;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8231cbddb6ed..9510cb0807bc 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -958,6 +958,7 @@ void napi_skb_free_stolen_head(struct sk_buff *skb)
 		nf_reset_ct(skb);
 		skb_dst_drop(skb);
 		skb_ext_put(skb);
+		skb_orphan(skb);
 		skb->slow_gro = 0;
 	}
 	napi_skb_cache_put(skb);
@@ -3898,6 +3899,9 @@ int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb)
 	NAPI_GRO_CB(p)->last = skb;
 	NAPI_GRO_CB(p)->count++;
 	p->data_len += skb->len;
+
+	/* sk owenrship - if any - completely transferred to the aggregated packet */
+	skb->destructor = NULL;
 	p->truesize += skb->truesize;
 	p->len += skb->len;
 
@@ -4265,6 +4269,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 	unsigned int headlen = skb_headlen(skb);
 	unsigned int len = skb_gro_len(skb);
 	unsigned int delta_truesize;
+	unsigned int new_truesize;
 	struct sk_buff *lp;
 
 	if (unlikely(p->len + len >= 65536 || NAPI_GRO_CB(skb)->flush))
@@ -4296,10 +4301,10 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 		skb_frag_size_sub(frag, offset);
 
 		/* all fragments truesize : remove (head size + sk_buff) */
-		delta_truesize = skb->truesize -
-				 SKB_TRUESIZE(skb_end_offset(skb));
+		new_truesize = SKB_TRUESIZE(skb_end_offset(skb));
+		delta_truesize = skb->truesize - new_truesize;
 
-		skb->truesize -= skb->data_len;
+		skb->truesize = new_truesize;
 		skb->len -= skb->data_len;
 		skb->data_len = 0;
 
@@ -4328,12 +4333,16 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
 		/* We dont need to clear skbinfo->nr_frags here */
 
-		delta_truesize = skb->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
+		new_truesize = SKB_TRUESIZE(sizeof(struct sk_buff));
+		delta_truesize = skb->truesize - new_truesize;
+		skb->truesize = new_truesize;
 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
 		goto done;
 	}
 
 merge:
+	/* sk owenrship - if any - completely transferred to the aggregated packet */
+	skb->destructor = NULL;
 	delta_truesize = skb->truesize;
 	if (offset > headlen) {
 		unsigned int eat = offset - headlen;
-- 
2.26.3

[PATCH net-next 6/6] veth: use skb_prepare_for_gro()

[Paolo Abeni]

Leveraging the previous patch we can now avoid orphaning the
skb in the veth gro path, allowing correct backpressure.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 drivers/net/veth.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 381670c08ba7..50eb43e5bf45 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -713,7 +713,7 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
 	int mac_len, delta, off;
 	struct xdp_buff xdp;
 
-	skb_orphan_partial(skb);
+	skb_prepare_for_gro(skb);
 
 	rcu_read_lock();
 	xdp_prog = rcu_dereference(rq->xdp_prog);
-- 
2.26.3

Re: [PATCH net-next 0/6] sk_buff: optimize GRO for the common case

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (refs/heads/master):

On Wed, 28 Jul 2021 18:23:58 +0200 you wrote:
> This is a trimmed down revision of "sk_buff: optimize layout for GRO",
> specifically dropping the changes to the sk_buff layout[1].
> 
> This series tries to accomplish 2 goals:
> - optimize the GRO stage for the most common scenario, avoiding a bunch
>   of conditional and some more code
> - let owned skbs entering the GRO engine, allowing backpressure in the
>   veth GRO forward path.
> 
> [...]

Here is the summary with links:
  - [net-next,1/6] sk_buff: introduce 'slow_gro' flags
    https://git.kernel.org/netdev/net-next/c/5fc88f93edf2
  - [net-next,2/6] sk_buff: track dst status in slow_gro
    https://git.kernel.org/netdev/net-next/c/8a886b142bd0
  - [net-next,3/6] sk_buff: track extension status in slow_gro
    https://git.kernel.org/netdev/net-next/c/b0999f385ac3
  - [net-next,4/6] net: optimize GRO for the common case.
    https://git.kernel.org/netdev/net-next/c/9efb4b5baf6c
  - [net-next,5/6] skbuff: allow 'slow_gro' for skb carring sock reference
    https://git.kernel.org/netdev/net-next/c/5e10da5385d2
  - [net-next,6/6] veth: use skb_prepare_for_gro()
    https://git.kernel.org/netdev/net-next/c/d504fff0d14a

You are awesome, thank you!
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