Decrease number of pointer derefs in connection.c

PATCH In review Jesper Juhl 2 participants 2 messages Dec 8, 2005 – Dec 9, 2005

Subsystems (2)

Networking Rxrpc sockets (AF_RXRPC)

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Jesper Juhl

author

2005-12-08 22:36 UTC #0 lore raw

PATCH 1/1 Decrease number of pointer derefs in connection.c

Hi,

Here's a small patch to decrease the number of pointer derefs in net/rxrpc/connection.c

Benefits of the patch:
- Fewer pointer dereferences should make the code slightly faster.
- Size of generated code is smaller
- improved readability

Please consider applying.

Signed-off-by Jesper Juhl <[email protected]>

---

 net/rxrpc/connection.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

orig:
text data bss dec hex filename
7146 40 4 7190 1c16 net/rxrpc/connection.o

patched:
text data bss dec hex filename
7140 40 4 7184 1c10 net/rxrpc/connection.o

net/rxrpc/connection.c +8 -6

@@ -220,6 +220,7 @@ int rxrpc_connection_lookup(struct rxrpc
 {
 	struct rxrpc_connection *conn, *candidate = NULL;
 	struct list_head *_p;
+	struct sk_buff *pkt = msg->pkt;
 	int ret, fresh = 0;
 	__be32 x_epoch, x_connid;
 	__be16 x_port, x_servid;

@@ -229,10 +230,10 @@ int rxrpc_connection_lookup(struct rxrpc
 	_enter("%p{{%hu}},%u,%hu",
 	       peer,
 	       peer->trans->port,
-	       ntohs(msg->pkt->h.uh->source),
+	       ntohs(pkt->h.uh->source),
 	       ntohs(msg->hdr.serviceId));
 
-	x_port		= msg->pkt->h.uh->source;
+	x_port		= pkt->h.uh->source;
 	x_epoch		= msg->hdr.epoch;
 	x_clflag	= msg->hdr.flags & RXRPC_CLIENT_INITIATED;
 	x_connid	= htonl(ntohl(msg->hdr.cid) & RXRPC_CIDMASK);

@@ -267,7 +268,7 @@ int rxrpc_connection_lookup(struct rxrpc
 		/* fill in the specifics */
 		candidate->addr.sin_family	= AF_INET;
 		candidate->addr.sin_port	= x_port;
-		candidate->addr.sin_addr.s_addr = msg->pkt->nh.iph->saddr;
+		candidate->addr.sin_addr.s_addr = pkt->nh.iph->saddr;
 		candidate->in_epoch		= x_epoch;
 		candidate->out_epoch		= x_epoch;
 		candidate->in_clientflag	= RXRPC_CLIENT_INITIATED;

@@ -675,6 +676,7 @@ int rxrpc_conn_receive_call_packet(struc
 				   struct rxrpc_message *msg)
 {
 	struct rxrpc_message *pmsg;
+	struct dst_entry *dst;
 	struct list_head *_p;
 	unsigned cix, seq;
 	int ret = 0;

@@ -710,10 +712,10 @@ int rxrpc_conn_receive_call_packet(struc
 
 	call->pkt_rcv_count++;
 
-	if (msg->pkt->dst && msg->pkt->dst->dev)
+	dst = msg->pkt->dst;
+	if (dst && dst->dev)
 		conn->peer->if_mtu =
-			msg->pkt->dst->dev->mtu -
-			msg->pkt->dst->dev->hard_header_len;
+			dst->dev->mtu - dst->dev->hard_header_len;
 
 	/* queue on the call in seq order */
 	rxrpc_get_message(msg);

David Howells

maintainer

2005-12-09 10:18 UTC #1 lore raw

Quoted 4 lines · Jesper Juhl

Benefits of the patch:
- Fewer pointer dereferences should make the code slightly faster.
- Size of generated code is smaller
- improved readability

I'm a little surprised that it makes it faster or smaller: I'd've thought that the gcc optimiser would be up to caching the pointer; in fact, if it made any difference, I'd've thought it'd make it larger, slower and consume more stack space as the compiler would then have to carry the extra variable around.

OTOH, compiler's are black magic, possibly even blacker than kernels, so who knows...

David