Date: Wed, 08 Sep 2004 11:26:16 -0700 From: Julian Elischer <julian@elischer.org> To: Bruce M Simpson <bms@spc.org> Cc: tcpdump-workers@tcpdump.org Subject: Re: [PATCH] Add ioctl to disable bpf timestamping Message-ID: <413F4EC8.8030401@elischer.org> In-Reply-To: <20040908092624.GD793@empiric.icir.org> References: <20040908092624.GD793@empiric.icir.org>
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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 */
>
>
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