tcpdump mailing list archives
Re: [RFC PATCH 0/2]: hw timestamp support
From: "Mcmillan, Scott A" <scott.a.mcmillan () intel com>
Date: Wed, 26 May 2010 09:03:59 -0700
Guy, Both the 'raw' and 'nic' timestamps are in the form of seconds since the Unix epoch, plus fractions of a second. Please see my response to Darren for more info on the difference between these two timestamp sources. The only reason I can think of to use 'raw' is for debugging. Regarding whether one would always want to use hw timestamps if they are available... I think in general, one would want to use hw timestamps. The reason I didn't make it the default is that limitations of current hw can lead to potentially confusing results. For example, the Intel 82580 nic only hw timestamps RX general purpose packets, meaning TX general purpose packets are still timestamped in sw. Hence, timestamps may not be monotonic in a capture stream (although RX timestamps will be monotonic and TX timestamps will be monotonic). If the consensus is to use hw timestamps by default if available, I have no issues modifying the patch accordingly. Similarly, if the 'raw' timesource is not seen as potentially useful, I can change that too. Scott -----Original Message----- From: tcpdump-workers-owner () lists tcpdump org [mailto:tcpdump-workers-owner () lists tcpdump org] On Behalf Of Guy Harris Sent: Tuesday, May 25, 2010 8:37 PM To: tcpdump-workers () lists tcpdump org Subject: Re: [tcpdump-workers] [RFC PATCH 0/2]: hw timestamp support On May 24, 2010, at 7:26 AM, Mcmillan, Scott A wrote:
[My apologies if this double posts. The mail server didn't care for the first submission.] This patch adds the capability to select the packet timestamp source.
Is there ever any reason *NOT* to use the hardware timestamp if it's available?
A new command line option was added to tcpdump, -j, to specify the source of the packet timestamp. Valid options are 'raw' to use the raw NIC HW timestamp and 'nic' to use the NIC HW timestamp transformed into the system clock basis.
Is the raw timestamp in the form of seconds since January 1, 1970, 00:00:00 UTC, plus fractions of a second? I assume "NIC HW timestamp transformed into the system clock basis" means that the time stamp in question *is* in the form of seconds since January 1, 1970, 00:00:00 UTC, plus fractions of a second? If "raw" is not in that form, and "nic" is in that form, is there any reason to use "raw"?- This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe. - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
Current thread:
- [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (May 24)
- Re: [RFC PATCH 0/2]: hw timestamp support yon ar c'hall (May 25)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (May 25)
- Re: [RFC PATCH 0/2]: hw timestamp support Darren Reed (May 25)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (May 26)
- Re: [RFC PATCH 0/2]: hw timestamp support Darren Reed (May 26)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (May 25)
- Re: [RFC PATCH 0/2]: hw timestamp support yon ar c'hall (May 25)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (May 26)
- Re: [RFC PATCH 0/2]: hw timestamp support Aaron Turner (May 26)
- Re: [RFC PATCH 0/2]: hw timestamp support Guy Harris (May 28)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (Jun 01)
- Re: [RFC PATCH 0/2]: hw timestamp support Mcmillan, Scott A (Jun 03)