[PATCH] Add ioctl to disable bpf timestamping

[Julian Elischer]

how much bandwidth  change does this give?
is teh timestamp really a big load?  fo a 4% increase I wouldn't bother.
for a 50% increase I would..


Bruce M Simpson wrote:

>Here's a patch against 5.3 to add a per-instance switch which allows
>the user to specify if captured packets should be timestamped (and,
>if so, whether microtime() or the faster but less accurate
>getmicrotime() call should be used).
>
>Comments/flames/etc to the usual...
>
>BMS
>  
>
>------------------------------------------------------------------------
>
>Index: bpf.c
>===================================================================
>RCS file: /home/ncvs/src/sys/net/bpf.c,v
>retrieving revision 1.130
>diff -u -p -r1.130 bpf.c
>--- bpf.c	5 Jul 2004 16:28:31 -0000	1.130
>+++ bpf.c	8 Sep 2004 09:22:09 -0000
>@@ -347,6 +347,7 @@ bpfopen(dev, flags, fmt, td)
> 	d->bd_bufsize = bpf_bufsize;
> 	d->bd_sig = SIGIO;
> 	d->bd_seesent = 1;
>+	d->bd_tstamp = BPF_TSTAMP_MICROTIME;
> #ifdef MAC
> 	mac_init_bpfdesc(d);
> 	mac_create_bpfdesc(td->td_ucred, d);
>@@ -629,6 +630,7 @@ reset_d(d)
>  *  BIOCSHDRCMPLT	Set "header already complete" flag
>  *  BIOCGSEESENT	Get "see packets sent" flag
>  *  BIOCSSEESENT	Set "see packets sent" flag
>+ *  BIOCSTSTAMP		Set "timestamp preference" flag
>  */
> /* ARGSUSED */
> static	int
>@@ -880,6 +882,13 @@ bpfioctl(dev, cmd, addr, flags, td)
> 		d->bd_seesent = *(u_int *)addr;
> 		break;
> 
>+	/*
>+	 * Set "timestamp preference" flag
>+	 */
>+	case BIOCSTSTAMP:
>+		d->bd_tstamp = *(u_int *)addr;
>+		break;
>+
> 	case FIONBIO:		/* Non-blocking I/O */
> 		break;
> 
>@@ -1331,7 +1340,14 @@ catchpacket(d, pkt, pktlen, snaplen, cpf
> 	 * Append the bpf header.
> 	 */
> 	hp = (struct bpf_hdr *)(d->bd_sbuf + curlen);
>-	microtime(&hp->bh_tstamp);
>+	/*
>+	 * Only prepend a timestamp if instructed to do so.
>+	 * getmicrotime() is less accurate but potentially faster.
>+	 */
>+	if (d->bd_tstamp == BPF_TSTAMP_MICROTIME)
>+		microtime(&hp->bh_tstamp);
>+	else if (d->bd_tstamp == BPF_TSTAMP_GETMICROTIME)
>+		getmicrotime(&hp->bh_tstamp);
> 	hp->bh_datalen = pktlen;
> 	hp->bh_hdrlen = hdrlen;
> 	/*
>Index: bpf.h
>===================================================================
>RCS file: /home/ncvs/src/sys/net/bpf.h,v
>retrieving revision 1.36
>diff -u -p -r1.36 bpf.h
>--- bpf.h	30 May 2004 17:03:48 -0000	1.36
>+++ bpf.h	8 Sep 2004 09:15:35 -0000
>@@ -113,6 +113,7 @@ struct bpf_version {
> #define BIOCSSEESENT	_IOW('B',119, u_int)
> #define	BIOCSDLT	_IOW('B',120, u_int)
> #define	BIOCGDLTLIST	_IOWR('B',121, struct bpf_dltlist)
>+#define	BIOCSTSTAMP	_IOW('B',122, u_int)
> 
> /*
>  * Structure prepended to each packet.
>@@ -491,4 +492,13 @@ u_int	 bpf_filter(const struct bpf_insn 
>  */
> #define BPF_MEMWORDS 16
> 
>+/*
>+ * Defines to specify timestamping preference for a BPF instance.
>+ * BPF_TSTAMP_MICROTIME is the default when none is specified.
>+ * Other settings may increase BPF capture performance under load.
>+ */
>+#define BPF_TSTAMP_NONE			0x00	/* Don't timestamp packets */
>+#define BPF_TSTAMP_MICROTIME		0x01	/* Use microtime() (slower) */
>+#define BPF_TSTAMP_GETMICROTIME		0x02	/* Use getmicrotime() */
>+
> #endif /* _NET_BPF_H_ */
>Index: bpfdesc.h
>===================================================================
>RCS file: /home/ncvs/src/sys/net/bpfdesc.h,v
>retrieving revision 1.27
>diff -u -p -r1.27 bpfdesc.h
>--- bpfdesc.h	7 Apr 2004 20:46:11 -0000	1.27
>+++ bpfdesc.h	8 Sep 2004 09:17:16 -0000
>@@ -73,6 +73,7 @@ struct bpf_d {
> 	u_char		bd_promisc;	/* true if listening promiscuously */
> 	u_char		bd_state;	/* idle, waiting, or timed out */
> 	u_char		bd_immediate;	/* true to return on packet arrival */
>+	u_char		bd_tstamp;	/* timestamping preferences */
> 	int		bd_hdrcmplt;	/* false to fill in src lladdr automatically */
> 	int		bd_seesent;	/* true if bpf should see sent packets */
> 	int		bd_async;	/* non-zero if packet reception should generate signal */
>  
>