diff mbox series

[v3,1/2] gro: decrease size of CB

Message ID 20230313162956.GA17242@debian (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series gro: optimise redundant parsing of packets | expand

Checks

Context Check Description
netdev/series_format warning Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 38 this patch: 38
netdev/cc_maintainers success CCed 7 of 7 maintainers
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 38 this patch: 38
netdev/checkpatch warning WARNING: line length of 89 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline fail Was 0 now: 1

Commit Message

Richard Gobert March 13, 2023, 4:30 p.m. UTC
The GRO control block (NAPI_GRO_CB) is currently at its maximum size.  This
commit reduces its size by putting two groups of fields that are used only
at different times into a union.

Specifically, the fields frag0 and frag0_len are the fields that make up
the frag0 optimisation mechanism, which is used during the initial parsing
of the SKB.

The fields last and age are used after the initial parsing, while the SKB
is stored in the GRO list, waiting for other packets to arrive.

There was one location in dev_gro_receive that modified the frag0 fields
after setting last and age. I changed this accordingly without altering the
code behaviour.

Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
---
 include/net/gro.h | 26 ++++++++++++++++----------
 net/core/gro.c    | 18 +++++++++++-------
 2 files changed, 27 insertions(+), 17 deletions(-)

Comments

Eric Dumazet March 13, 2023, 5:01 p.m. UTC | #1
On Mon, Mar 13, 2023 at 9:30 AM Richard Gobert <richardbgobert@gmail.com> wrote:
>
> The GRO control block (NAPI_GRO_CB) is currently at its maximum size.  This
> commit reduces its size by putting two groups of fields that are used only
> at different times into a union.
>
> Specifically, the fields frag0 and frag0_len are the fields that make up
> the frag0 optimisation mechanism, which is used during the initial parsing
> of the SKB.

Note that these fields could also be stored in some auto variable,
instead of skb.

>
> The fields last and age are used after the initial parsing, while the SKB
> is stored in the GRO list, waiting for other packets to arrive.
>
> There was one location in dev_gro_receive that modified the frag0 fields
> after setting last and age. I changed this accordingly without altering the
> code behaviour.
>
> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
> ---

SGTM, thanks.

Reviewed-by: Eric Dumazet <edumazet@google.com>
diff mbox series

Patch

diff --git a/include/net/gro.h b/include/net/gro.h
index a4fab706240d..7b47dd6ce94f 100644
--- a/include/net/gro.h
+++ b/include/net/gro.h
@@ -11,11 +11,23 @@ 
 #include <net/udp.h>
 
 struct napi_gro_cb {
-	/* Virtual address of skb_shinfo(skb)->frags[0].page + offset. */
-	void	*frag0;
+	union {
+		struct {
+			/* Virtual address of skb_shinfo(skb)->frags[0].page + offset. */
+			void	*frag0;
 
-	/* Length of frag0. */
-	unsigned int frag0_len;
+			/* Length of frag0. */
+			unsigned int frag0_len;
+		};
+
+		struct {
+			/* used in skb_gro_receive() slow path */
+			struct sk_buff *last;
+
+			/* jiffies when first packet was created/queued */
+			unsigned long age;
+		};
+	};
 
 	/* This indicates where we are processing relative to skb->data. */
 	int	data_offset;
@@ -32,9 +44,6 @@  struct napi_gro_cb {
 	/* Used in ipv6_gro_receive() and foo-over-udp */
 	u16	proto;
 
-	/* jiffies when first packet was created/queued */
-	unsigned long age;
-
 /* Used in napi_gro_cb::free */
 #define NAPI_GRO_FREE             1
 #define NAPI_GRO_FREE_STOLEN_HEAD 2
@@ -77,9 +86,6 @@  struct napi_gro_cb {
 
 	/* used to support CHECKSUM_COMPLETE for tunneling protocols */
 	__wsum	csum;
-
-	/* used in skb_gro_receive() slow path */
-	struct sk_buff *last;
 };
 
 #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)
diff --git a/net/core/gro.c b/net/core/gro.c
index a606705a0859..b1fdabd414a5 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -460,6 +460,14 @@  static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
 	}
 }
 
+static inline void gro_try_pull_from_frag0(struct sk_buff *skb)
+{
+	int grow = skb_gro_offset(skb) - skb_headlen(skb);
+
+	if (grow > 0)
+		gro_pull_from_frag0(skb, grow);
+}
+
 static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 {
 	struct sk_buff *oldest;
@@ -489,7 +497,6 @@  static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	struct sk_buff *pp = NULL;
 	enum gro_result ret;
 	int same_flow;
-	int grow;
 
 	if (netif_elide_gro(skb->dev))
 		goto normal;
@@ -564,17 +571,13 @@  static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	else
 		gro_list->count++;
 
+	gro_try_pull_from_frag0(skb);
 	NAPI_GRO_CB(skb)->age = jiffies;
 	NAPI_GRO_CB(skb)->last = skb;
 	if (!skb_is_gso(skb))
 		skb_shinfo(skb)->gso_size = skb_gro_len(skb);
 	list_add(&skb->list, &gro_list->list);
 	ret = GRO_HELD;
-
-pull:
-	grow = skb_gro_offset(skb) - skb_headlen(skb);
-	if (grow > 0)
-		gro_pull_from_frag0(skb, grow);
 ok:
 	if (gro_list->count) {
 		if (!test_bit(bucket, &napi->gro_bitmask))
@@ -587,7 +590,8 @@  static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 
 normal:
 	ret = GRO_NORMAL;
-	goto pull;
+	gro_try_pull_from_frag0(skb);
+	goto ok;
 }
 
 struct packet_offload *gro_find_receive_by_type(__be16 type)