Commit de5a1f3c authored by Paolo Abeni's avatar Paolo Abeni Committed by David S. Miller
Browse files

net: gro: minor optimization for dev_gro_receive() 



While inspecting some perf report, I noticed that the compiler
emits suboptimal code for the napi CB initialization, fetching
and storing multiple times the memory for flags bitfield.
This is with gcc 10.3.1, but I observed the same with older compiler
versions.

We can help the compiler to do a nicer work clearing several
fields at once using an u32 alias. The generated code is quite
smaller, with the same number of conditional.

Before:
objdump -t net/core/gro.o | grep " F .text"
0000000000000bb0 l     F .text	0000000000000357 dev_gro_receive

After:
0000000000000bb0 l     F .text	000000000000033c dev_gro_receive

v1  -> v2:
 - use struct_group (Alexander and Alex)

RFC -> v1:
 - use __struct_group to delimit the zeroed area (Alexander)

Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7881453e

include/net/gro.h

+28 −24
Original line number Diff line number Diff line
@@ -29,14 +29,17 @@ struct napi_gro_cb { 
	/* Number of segments aggregated. */

	u16	count;



	/* Start offset for remote checksum offload */

	u16	gro_remcsum_start;

	/* Used in ipv6_gro_receive() and foo-over-udp */

	u16	proto;



	/* jiffies when first packet was created/queued */

	unsigned long age;



	/* Used in ipv6_gro_receive() and foo-over-udp */

	u16	proto;

	/* portion of the cb set to zero at every gro iteration */

	struct_group(zeroed,



		/* Start offset for remote checksum offload */

		u16	gro_remcsum_start;



		/* This is non-zero if the packet may be of the same flow. */

		u8	same_flow:1;
@@ -69,6 +72,7 @@ struct napi_gro_cb { 


		/* GRO is done by frag_list pointer chaining. */

		u8	is_flist:1;

	);



	/* used to support CHECKSUM_COMPLETE for tunneling protocols */

	__wsum	csum;

net/core/gro.c

+4 −11
Original line number Diff line number Diff line
@@ -459,29 +459,22 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff 


		skb_set_network_header(skb, skb_gro_offset(skb));

		skb_reset_mac_len(skb);

		NAPI_GRO_CB(skb)->same_flow = 0;

		BUILD_BUG_ON(sizeof_field(struct napi_gro_cb, zeroed) != sizeof(u32));

		BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed),

					 sizeof(u32))); /* Avoid slow unaligned acc */

		*(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0;

		NAPI_GRO_CB(skb)->flush = skb_is_gso(skb) || skb_has_frag_list(skb);

		NAPI_GRO_CB(skb)->free = 0;

		NAPI_GRO_CB(skb)->encap_mark = 0;

		NAPI_GRO_CB(skb)->recursion_counter = 0;

		NAPI_GRO_CB(skb)->is_fou = 0;

		NAPI_GRO_CB(skb)->is_atomic = 1;

		NAPI_GRO_CB(skb)->gro_remcsum_start = 0;



		/* Setup for GRO checksum validation */

		switch (skb->ip_summed) {

		case CHECKSUM_COMPLETE:

			NAPI_GRO_CB(skb)->csum = skb->csum;

			NAPI_GRO_CB(skb)->csum_valid = 1;

			NAPI_GRO_CB(skb)->csum_cnt = 0;

			break;

		case CHECKSUM_UNNECESSARY:

			NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1;

			NAPI_GRO_CB(skb)->csum_valid = 0;

			break;

		default:

			NAPI_GRO_CB(skb)->csum_cnt = 0;

			NAPI_GRO_CB(skb)->csum_valid = 0;

		}



		pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive,