Skip to contentSkip to conversation

Avoid gettimeofday when not needed

PATCH In review Andi Kleen 5 participants 10 messages Mar 31, 2004

Subsystems (11)
Networking Network drivers NFS client NFS server +7 more subsystems
lore
Share & tools
lore

Andi Kleen

author
#0 lore raw

PATCH 1/1 Avoid gettimeofday when not needed

This patch implements an optimization I proposed a long time ago. gettimeofday can be quite costly and it currently is on the fast path of every packet. Normally the packet time stamp is not needed (e.g. TCP doesn't use it), except for tcpdump and a few applications.

This patch adds a global counter that is enabled only when some socket is interested in time stamps. There is a small race window after enabling the timestamp when there are already packets queued without timestamp. In this case just the current time is filled in. For simplicity the counter is only decremented after the socket has been destroyed again.

sunrpc was using the timestamp too, but I just changed it to use xtime (which is accurate enough and true end2end latency including host latencies is better anyways)

The patch deletes nearly as much code as it adds because it cleans up a lot of duplicated code in various socket disciplines.

I didn't benchmark much (mostly because all my machines have quite fast gettimeofday), some feedback on how much it helps would be appreciated (especially on machines with slow gettimeofday, like IBM summit or Altix)

One warning: bind9 seems to enable the time stamp. If you do benchmarks kill the name server. This should be probably fixed in user space.

Most of the patch is quite straight forward, except for the change in the v4/v6 proxy arp code. I assume it was checking the time stamp to distingush locally originated packets from external packets (?). I changed it to use skb->sk instead. I'm not 100% sure if I guessed the intention correctly and don't know why it should check that anyways. Someone should review that change.

-Andi

include/net/sock.h renamed from include/net/sock.h-T +28 -5
diff -u linux-2.6.5rc3-averell/include/net/sock.h-T linux-2.6.5rc3-averell/include/net/sock.h
@@ -382,6 +382,7 @@
 	SOCK_LINGER,
 	SOCK_DESTROY,
 	SOCK_BROADCAST,
+	SOCK_TIMESTAMP,
 };
 
 static inline void sock_set_flag(struct sock *sk, enum sock_flags flag)

@@ -1023,11 +1024,33 @@
 static __inline__ void
 sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
 {
-	if (sk->sk_rcvtstamp)
-		put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMP, sizeof(skb->stamp), &skb->stamp);
-	else
-		sk->sk_stamp = skb->stamp;
-}
+	struct timeval *stamp = &skb->stamp;
+	if (sk->sk_rcvtstamp) { 
+		/* Race occurred between timestamp enabling and packet
+		   receiving.  Fill in the current time for now. */
+		if (stamp->tv_sec == 0)
+			do_gettimeofday(stamp);
+		put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMP, sizeof(struct timeval),
+			 stamp);
+	} else
+		sk->sk_stamp = *stamp;
+}
+
+extern atomic_t netstamp_needed;
+extern void sock_enable_timestamp(struct sock *sk);
+extern void sock_disable_timestamp(struct sock *sk);
+
+static inline void net_timestamp(struct timeval *stamp) 
+{ 
+	if (atomic_read(&netstamp_needed)) 
+		do_gettimeofday(stamp);
+	else {
+		stamp->tv_sec = 0;
+		stamp->tv_usec = 0;
+	}		
+} 
+
+extern int sock_get_timestamp(struct sock *, struct timeval *);
 
 /* 
  *	Enable debug/info messages
net/core/sock.c renamed from net/core/sock.c-T +41 -1

68 lines not on this page · raw message

net/core/dev.c renamed from net/core/dev.c-T +4 -4
diff -u linux-2.6.5rc3-averell/net/core/dev.c-T linux-2.6.5rc3-averell/net/core/dev.c
@@ -1125,7 +1125,7 @@
 void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct packet_type *ptype;
-	do_gettimeofday(&skb->stamp);
+	net_timestamp(&skb->stamp);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(ptype, &ptype_all, list) {

@@ -1546,9 +1546,9 @@
 		return NET_RX_DROP;
 	}
 #endif
-
+	
 	if (!skb->stamp.tv_sec)
-		do_gettimeofday(&skb->stamp);
+		net_timestamp(&skb->stamp);
 
 	/*
 	 * The code is rearranged so that the path is the most

@@ -1710,7 +1710,7 @@
 #endif
 
 	if (!skb->stamp.tv_sec)
-		do_gettimeofday(&skb->stamp);
+		net_timestamp(&skb->stamp);
 
 	skb_bond(skb);
net/ipv4/af_inet.c renamed from net/ipv4/af_inet.c-T +1 -5
diff -u linux-2.6.5rc3-averell/net/ipv4/af_inet.c-T linux-2.6.5rc3-averell/net/ipv4/af_inet.c
@@ -843,11 +843,7 @@
 
 	switch (cmd) {
 		case SIOCGSTAMP:
-			if (!sk->sk_stamp.tv_sec)
-				err = -ENOENT;
-			else if (copy_to_user((void *)arg, &sk->sk_stamp,
-					      sizeof(struct timeval)))
-				err = -EFAULT;
+			err = sock_get_timestamp(sk, (struct timeval *)arg);
 			break;
 		case SIOCADDRT:
 		case SIOCDELRT:
net/ipv4/arp.c renamed from net/ipv4/arp.c-T +11 -1
diff -u linux-2.6.5rc3-averell/net/ipv4/arp.c-T linux-2.6.5rc3-averell/net/ipv4/arp.c
@@ -860,7 +860,17 @@
 				if (n)
 					neigh_release(n);
 
-				if (skb->stamp.tv_sec == 0 ||
+				/* Previous code here tested 
+				   skb->stamp.tv_sec != 0. I can only guess
+				   what the author intended with this -
+				   maybe check for packets that have originated
+				   locally. Most likely it was a bug because
+				   there are all kinds of situations where
+				   even a local packet can have a stamp.
+				   It is replaced with an ->sk check
+				   now, which also won't trigger for 
+				   received packets. -AK */
+				if (skb->sk != NULL || 
 				    skb->pkt_type == PACKET_HOST ||
 				    in_dev->arp_parms->proxy_delay == 0) {
 					arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha);
net/sunrpc/svcsock.c renamed from net/sunrpc/svcsock.c-T +6 -0
diff -u linux-2.6.5rc3-averell/net/sunrpc/svcsock.c-T linux-2.6.5rc3-averell/net/sunrpc/svcsock.c
@@ -591,6 +591,12 @@
 		/* possibly an icmp error */
 		dprintk("svc: recvfrom returned error %d\n", -err);
 	}
+	if (skb->stamp.tv_sec == 0) {
+		skb->stamp.tv_sec = xtime.tv_sec; 
+		skb->stamp.tv_usec = xtime.tv_nsec * 1000; 
+		/* Don't enable netstamp, sunrpc doesn't 
+		   need that much accuracy */
+	}
 	svsk->sk_sk->sk_stamp = skb->stamp;
 	set_bit(SK_DATA, &svsk->sk_flags); /* there may be more data... */
net/rose/af_rose.c renamed from net/rose/af_rose.c-T +2 -6
diff -u linux-2.6.5rc3-averell/net/rose/af_rose.c-T linux-2.6.5rc3-averell/net/rose/af_rose.c
@@ -1269,12 +1269,8 @@
 	}
 
 	case SIOCGSTAMP:
-		if (sk != NULL) {
-			if (!sk->sk_stamp.tv_sec)
-				return -ENOENT;
-			return copy_to_user((void *)arg, &sk->sk_stamp,
-					  sizeof(struct timeval)) ? -EFAULT : 0;
-		}
+		if (sk != NULL) 
+			return sock_get_timestamp(sk, (struct timeval *)arg);
 		return -EINVAL;
 
 	case SIOCGIFADDR:
net/irda/af_irda.c renamed from net/irda/af_irda.c-T +2 -8
diff -u linux-2.6.5rc3-averell/net/irda/af_irda.c-T linux-2.6.5rc3-averell/net/irda/af_irda.c
@@ -1796,14 +1796,8 @@
 	}
 
 	case SIOCGSTAMP:
-		if (sk != NULL) {
-			if (!sk->sk_stamp.tv_sec)
-				return -ENOENT;
-			if (copy_to_user((void *)arg, &sk->sk_stamp,
-					 sizeof(struct timeval)))
-				return -EFAULT;
-			return 0;
-		}
+		if (sk != NULL)
+			return sock_get_timestamp(sk, (struct timeval *)arg);
 		return -EINVAL;
 
 	case SIOCGIFADDR:
net/ipx/af_ipx.c renamed from net/ipx/af_ipx.c-T +4 -10
diff -u linux-2.6.5rc3-averell/net/ipx/af_ipx.c-T linux-2.6.5rc3-averell/net/ipx/af_ipx.c
@@ -1797,7 +1797,8 @@
 				     copied);
 	if (rc)
 		goto out_free;
-	sk->sk_stamp = skb->stamp;
+	if (skb->stamp.tv_sec)
+		sk->sk_stamp = skb->stamp;
 
 	msg->msg_namelen = sizeof(*sipx);
 

@@ -1870,15 +1871,8 @@
 		break;
 	case SIOCGSTAMP:
 		rc = -EINVAL;
-		if (sk) {
-			rc = -ENOENT;
-			if (!sk->sk_stamp.tv_sec)
-				break;
-			rc = -EFAULT;
-			if (!copy_to_user((void *)arg, &sk->sk_stamp,
-					  sizeof(struct timeval)))
-				rc = 0;
-		}
+		if (sk) 
+			rc = sock_get_timestamp(sk, (struct timeval *)arg);
 		break;
 	case SIOCGIFDSTADDR:
 	case SIOCSIFDSTADDR:
net/atm/ioctl.c renamed from net/atm/ioctl.c-T +2 -6
diff -u linux-2.6.5rc3-averell/net/atm/ioctl.c-T linux-2.6.5rc3-averell/net/atm/ioctl.c
@@ -76,12 +76,8 @@
 				goto done;
 			}
 		case SIOCGSTAMP: /* borrowed from IP */
-			if (!vcc->sk->sk_stamp.tv_sec) {
-				error = -ENOENT;
-				goto done;
-			}
-			error = copy_to_user((void *)arg, &vcc->sk->sk_stamp,
-					     sizeof(struct timeval)) ? -EFAULT : 0;
+			error = sock_get_timestamp(vcc->sk, (struct timeval *)
+						   arg);
 			goto done;
 		case ATM_SETSC:
 			printk(KERN_WARNING "ATM_SETSC is obsolete\n");
net/ax25/af_ax25.c renamed from net/ax25/af_ax25.c-T +1 -6
diff -u linux-2.6.5rc3-averell/net/ax25/af_ax25.c-T linux-2.6.5rc3-averell/net/ax25/af_ax25.c
@@ -1694,12 +1694,7 @@
 
 	case SIOCGSTAMP:
 		if (sk != NULL) {
-			if (!sk->sk_stamp.tv_sec) {
-				res = -ENOENT;
-				break;
-			}
-			res = copy_to_user((void *)arg, &sk->sk_stamp,
-					  sizeof(struct timeval)) ? -EFAULT : 0;
+			res = sock_get_timestamp(sk, (struct timeval *)arg);
 			break;
 	 	}
 		res = -EINVAL;
net/ipv6/af_inet6.c renamed from net/ipv6/af_inet6.c-T +1 -7
diff -u linux-2.6.5rc3-averell/net/ipv6/af_inet6.c-T linux-2.6.5rc3-averell/net/ipv6/af_inet6.c
@@ -474,13 +474,7 @@
 	switch(cmd) 
 	{
 	case SIOCGSTAMP:
-		if (!sk->sk_stamp.tv_sec)
-			return -ENOENT;
-		err = copy_to_user((void *)arg, &sk->sk_stamp,
-				   sizeof(struct timeval));
-		if (err)
-			return -EFAULT;
-		return 0;
+		return sock_get_timestamp(sk, (struct timeval *)arg);
 
 	case SIOCADDRT:
 	case SIOCDELRT:
net/ipv6/ndisc.c renamed from net/ipv6/ndisc.c-T +2 -1
diff -u linux-2.6.5rc3-averell/net/ipv6/ndisc.c-T linux-2.6.5rc3-averell/net/ipv6/ndisc.c
@@ -761,7 +761,8 @@
 		if (ipv6_chk_acast_addr(dev, &msg->target) ||
 		    (idev->cnf.forwarding && 
 		     pneigh_lookup(&nd_tbl, &msg->target, dev, 0))) {
-			if (skb->stamp.tv_sec != 0 &&
+			/* See comment in arp.c about the weird sk check */
+			if (skb->sk == NULL &&
 			    skb->pkt_type != PACKET_HOST &&
 			    inc != 0 &&
 			    idev->nd_parms->proxy_delay != 0) {
net/rxrpc/transport.c renamed from net/rxrpc/transport.c-T +5 -0
diff -u linux-2.6.5rc3-averell/net/rxrpc/transport.c-T linux-2.6.5rc3-averell/net/rxrpc/transport.c
@@ -341,6 +341,11 @@
 	msg->trans = trans;
 	msg->state = RXRPC_MSG_RECEIVED;
 	msg->stamp = pkt->stamp;
+	if (msg->stamp.tv_sec == 0) {
+		do_gettimeofday(&msg->stamp); 
+		if (skb->sk) 
+			sock_enable_netstamp(skb->sk);
+	} 
 	msg->seq = ntohl(msg->hdr.seq);
 
 	/* attach the packet */
net/sctp/input.c renamed from net/sctp/input.c-T +6 -0
diff -u linux-2.6.5rc3-averell/net/sctp/input.c-T linux-2.6.5rc3-averell/net/sctp/input.c
@@ -175,6 +175,12 @@
 	rcvr = asoc ? &asoc->base : &ep->base;
 	sk = rcvr->sk;
 
+	/* SCTP seems to always need a timestamp right now (FIXME) */
+	if (skb->stamp.tv_sec == 0) {
+		do_gettimeofday(&skb->stamp);
+		sock_enable_timestamp(sk); 
+	}
+
 	if (!xfrm_policy_check(sk, XFRM_POLICY_IN, skb, family))
 		goto discard_release;
net/x25/af_x25.c renamed from net/x25/af_x25.c-T +3 -7
diff -u linux-2.6.5rc3-averell/net/x25/af_x25.c-T linux-2.6.5rc3-averell/net/x25/af_x25.c
@@ -1206,14 +1206,10 @@
 		}
 
 		case SIOCGSTAMP:
-			if (sk) {
-				rc = -ENOENT;
-				if (!sk->sk_stamp.tv_sec)
-					break;
-				rc = copy_to_user((void *)arg, &sk->sk_stamp,
-						  sizeof(struct timeval)) ? -EFAULT : 0;
-			}
 			rc = -EINVAL;
+			if (sk)
+				rc = sock_get_timestamp(sk, 
+						(struct timeval *)arg); 
 			break;
 		case SIOCGIFADDR:
 		case SIOCSIFADDR:
net/wanrouter/af_wanpipe.c renamed from net/wanrouter/af_wanpipe.c-T +1 -7
diff -u linux-2.6.5rc3-averell/net/wanrouter/af_wanpipe.c-T linux-2.6.5rc3-averell/net/wanrouter/af_wanpipe.c
@@ -1765,13 +1765,7 @@
 	switch(cmd) 
 	{
 		case SIOCGSTAMP:
-			if (!sk->sk_stamp.tv_sec)
-				return -ENOENT;
-			err = -EFAULT;
-			if (!copy_to_user((void *)arg, &sk->sk_stamp,
-			    sizeof(struct timeval)))
-				err = 0;
-			return err;
+			return sock_get_timestamp(sk, (struct timeval *)arg);
 
 		case SIOC_WANPIPE_CHECK_TX:
net/packet/af_packet.c renamed from net/packet/af_packet.c-T +6 -7
diff -u linux-2.6.5rc3-averell/net/packet/af_packet.c-T linux-2.6.5rc3-averell/net/packet/af_packet.c
@@ -606,6 +606,10 @@
 	h->tp_snaplen = snaplen;
 	h->tp_mac = macoff;
 	h->tp_net = netoff;
+	if (skb->stamp.tv_sec == 0) { 
+		do_gettimeofday(&skb->stamp);
+		sock_enable_timestamp(sk);
+	}
 	h->tp_sec = skb->stamp.tv_sec;
 	h->tp_usec = skb->stamp.tv_usec;
 

@@ -1442,13 +1446,8 @@
 			return put_user(amount, (int *)arg);
 		}
 		case SIOCGSTAMP:
-			if (!sk->sk_stamp.tv_sec)
-				return -ENOENT;
-			if (copy_to_user((void *)arg, &sk->sk_stamp,
-					 sizeof(struct timeval)))
-				return -EFAULT;
-			break;
-
+			return sock_get_timestamp(sk, (struct timeval *)arg);
+			
 #ifdef CONFIG_INET
 		case SIOCADDRT:
 		case SIOCDELRT:
net/netrom/af_netrom.c renamed from net/netrom/af_netrom.c-T +4 -10
diff -u linux-2.6.5rc3-averell/net/netrom/af_netrom.c-T linux-2.6.5rc3-averell/net/netrom/af_netrom.c
@@ -1200,17 +1200,11 @@
 	}
 
 	case SIOCGSTAMP:
-		if (sk != NULL) {
-			if (!sk->sk_stamp.tv_sec) {
-				release_sock(sk);
-				return -ENOENT;
-			}
-			ret = copy_to_user((void *)arg, &sk->sk_stamp, sizeof(struct timeval)) ? -EFAULT : 0;
-			release_sock(sk);
-			return ret;
-		}
+		ret = -EINVAL;
+		if (sk != NULL)
+			ret = sock_get_timestamp(sk, (struct timeval *)arg);
 		release_sock(sk);
-		return -EINVAL;
+		return ret;
 
 	case SIOCGIFADDR:
 	case SIOCSIFADDR:
net/appletalk/ddp.c renamed from net/appletalk/ddp.c-T +1 -7
diff -u linux-2.6.5rc3-averell/net/appletalk/ddp.c-T linux-2.6.5rc3-averell/net/appletalk/ddp.c
@@ -1795,13 +1795,7 @@
 			break;
 		}
 		case SIOCGSTAMP:
-			if (!sk)
-				break;
-			rc = -ENOENT;
-			if (!sk->sk_stamp.tv_sec)
-				break;
-			rc = copy_to_user((void *)arg, &sk->sk_stamp,
-					  sizeof(struct timeval)) ? -EFAULT : 0;
+			rc = sock_get_timestamp(sk, (struct timeval *)arg);
 			break;
 		/* Routing */
 		case SIOCADDRT:
net/econet/af_econet.c renamed from net/econet/af_econet.c-T +2 -4
diff -u linux-2.6.5rc3-averell/net/econet/af_econet.c-T linux-2.6.5rc3-averell/net/econet/af_econet.c
@@ -665,10 +665,8 @@
 
 	switch(cmd) {
 		case SIOCGSTAMP:
-			if (!sk->sk_stamp.tv_sec)
-				return -ENOENT;
-			return copy_to_user((void *)arg, &sk->sk_stamp,
-					  sizeof(struct timeval)) ? -EFAULT : 0;
+			return sock_get_timestamp(sk,(struct timeval *)arg);
+
 		case SIOCSIFADDR:
 		case SIOCGIFADDR:
 			return ec_dev_ioctl(sock, cmd, (void *)arg);
#1 lore raw
Quoted 3 lines · Andi Kleen

This patch implements an optimization I proposed a long time ago. gettimeofday can be quite costly and it currently is on the fast path of every packet. Normally the packet time stamp is not needed (e.g. TCP doesn't use it), except for tcpdump
and a few applications.

Will this work for apps that don't use a seperate syscall to get the timestamp. Like CONFIG_PACKET_MMAP for e.g?

Pádraig.

author
#2 lore raw
Quoted 9 lines · On Wed, Mar 31, 2004 at 01:22:14PM +0100, [email protected] wrote:
Quoted 5 lines · Andi Kleen

This patch implements an optimization I proposed a long time ago. gettimeofday can be quite costly and it currently is on the fast path of every packet. Normally the packet time stamp is not needed (e.g. TCP doesn't use it), except for tcpdump and a few applications.

Will this work for apps that don't use a seperate syscall to get the timestamp. Like CONFIG_PACKET_MMAP for e.g?

The mmap will enable the time stamp, until the socket is closed.

-Andi

#3 lore raw
In reply to Andi Kleen

Hi Andi,

Quoted 6 lines · Andi Kleen

Most of the patch is quite straight forward, except for the change in the v4/v6 proxy arp code. I assume it was checking the time stamp to distingush locally originated packets from external packets (?). I changed it to use skb->sk instead. I'm not 100% sure if I guessed the intention correctly and don't know why it should check that anyways. Someone should review that change.

I suspect this breaks proxy arp/ndisc!

The arp/ndisc requests are queued up for a random time before being processed by the proxy. Check out pneigh_enqueue() in net/core/neighbour.c for details. The skb->stamp.tv_sec check was used to separate the locally re-fed requests from ones received from the net.

AFAICS, skb->sk isn't set for the enqueued packets, so checking the field doesn't make sense. One thing that instead *might* work, would be to set skb->pkt_type = PACKET_HOST in pneigh_enqueue().

Of course skb->pkt_type = PACKET_HOST is set in other places as well, so some falsely marked packets might bypass the required random delay. I don't think this is a big concern, but I thought it was best to bring it up...

Quoted 1 line

-Andi

Regards,
Ville
--
Ville Nuorvala
Research Assistant, Institute of Digital Communications, Helsinki University of Technology
email: [email protected], phone: +358 (0)9 451 5257

author
#4 lore raw
Quoted 6 lines

I suspect this breaks proxy arp/ndisc!

The arp/ndisc requests are queued up for a random time before being processed by the proxy. Check out pneigh_enqueue() in net/core/neighbour.c for details. The skb->stamp.tv_sec check was used to separate the locally re-fed requests from ones received from the net.

Ok, thanks for clarifying this. I guessed the intention wrong then.

A better way may be to just add a new skb flag for this that is managed by the arp code? Comments?

-Andi

#5 lore raw
Quoted 4 lines · Andi Kleen

Ok, thanks for clarifying this. I guessed the intention wrong then.

A better way may be to just add a new skb flag for this that is managed by the arp code? Comments?

I guess that's all right.

There just doesn't seem to be any general flag field in sk_buff that we might use at this moment. Should one be added, or should we just hide the flag inside the cb field using the likes of inet_skb_parm and inet6_skb_parm?

Quoted 1 line

-Andi

Regards,
Ville

--
Ville Nuorvala
Research Assistant, Institute of Digital Communications, Helsinki University of Technology
email: [email protected], phone: +358 (0)9 451 5257

author
#6 lore raw
Quoted 4 lines · Ville Nuorvala

There just doesn't seem to be any general flag field in sk_buff that we might use at this moment. Should one be added, or should we just hide the flag inside the cb field using the likes of inet_skb_parm and inet6_skb_parm?

There are no free bits indeed. I think ->cb is the best choice then.

-Andi

#7 lore raw
Quoted 9 lines · Andi Kleen
Quoted 4 lines · Ville Nuorvala

There just doesn't seem to be any general flag field in sk_buff that we might use at this moment. Should one be added, or should we just hide the flag inside the cb field using the likes of inet_skb_parm and inet6_skb_parm?

There are no free bits indeed. I think ->cb is the best choice then.

Why not add a 32-bit field to the skb to handle various flag needs going forward?

If space is very important, could use an uint16 for flags and consolidate the ip_summed and cloned fields, which seem to be boolean fields.

	unsigned char		local_df,
				cloned,
				pkt_type,
				ip_summed;

Ben

Signature · 2 lines
Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com
#8 lore raw
Quoted 9 lines · On Wed, 31 Mar 2004 09:30:02 -0800 Ben Greear <[email protected]> wrote:
Quoted 8 lines · Andi Kleen
Quoted 4 lines · Ville Nuorvala

There just doesn't seem to be any general flag field in sk_buff that we might use at this moment. Should one be added, or should we just hide the flag inside the cb field using the likes of inet_skb_parm and inet6_skb_parm?

Quoted 4 lines
Quoted 1 line

There are no free bits indeed. I think ->cb is the best choice then.

Why not add a 32-bit field to the skb to handle various flag needs going forward?

That is what ->cb already is

-Andi

#9 lore raw
Quoted 5 lines · Andi Kleen
Quoted 2 lines

Why not add a 32-bit field to the skb to handle various flag needs going forward?

That is what ->cb already is

From the comments, it appears each layer can write over these, and since it's just a block of bytes, it is difficult to understand what each bit/field is used for.

It still seems to me that a bit-field with well defined flags is more useful.

Ben

Signature · 2 lines
Ben Greear <[email protected]>
Candela Technologies Inc  http://www.candelatech.com