Date: Wed, 8 Sep 2004 12:00:29 -0700 From: Guy Harris <guy@alum.mit.edu> To: tcpdump-workers@lists.tcpdump.org Cc: freebsd-net@FreeBSD.org Subject: Re: [tcpdump-workers] [PATCH] Add ioctl to disable bpf timestamping Message-ID: <5A076AAC-01C9-11D9-8193-000A958097E4@alum.mit.edu> In-Reply-To: <20040908092624.GD793@empiric.icir.org> References: <20040908092624.GD793@empiric.icir.org>
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On Sep 8, 2004, at 2:26 AM, 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). This is probably a pointless optimization, as you probably relatively rarely have multiple BPF devices bound to the same interface receiving the bulk of the packets (as opposed to some daemon with a filter that passes only the packets it's interested in), but would there be any advantage to having "bpf_tap()" and "bpf_mtap()" fetch the time stamp and pass that to "catchpacket()", so that in the case where there *is* more than one tap, the time stamp is only fetched once? That has the "disadvantage" that a tap might get a more accurate time stamp than it needs (the most accurate time stamp requested by a BPF device would be the one used). > Comments/flames/etc to the usual... If this is generally accepted as a good idea, it might be worth mentioning it to the other BSDs.
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