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From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Vivien Didelot <vivien.didelot@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org, patrick.keroulas@radio-canada.ca, thomas@monjalon.net
Subject: Re: [dpdk-dev] [PATCH 1/2] net/pcap: support software Tx nanosecond timestamp
Date: Thu, 4 Jun 2020 11:52:16 +0100
Message-ID: <1a562b11-b666-e900-c345-ffccb71fdfe2@intel.com> (raw)
In-Reply-To: <20200603162652.GB13716@t480s.localdomain>

On 6/3/2020 9:26 PM, Vivien Didelot wrote:
> On Wed, 3 Jun 2020 13:11:39 -0700, Stephen Hemminger <stephen@networkplumber.org> wrote:
>> On Wed, 3 Jun 2020 18:50:51 +0100
>> Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>>
>>> On 5/23/2020 6:21 PM, Vivien Didelot wrote:
>>>> When capturing packets into a PCAP file, DPDK currently uses
>>>> microseconds for the timestamp. But libpcap supports interpreting
>>>> tv_usec as nanoseconds depending on the file timestamp precision.
>>>>
>>>> To support this, use PCAP_TSTAMP_PRECISION_NANO when creating the
>>>> empty PCAP file as specified by PCAP_OPEN_DEAD(3PCAP) and implement
>>>> nanosecond timeval addition. This also ensures that the precision
>>>> reported by capinfos is nanoseconds (9).  
>>>
>>> Overall good idea and patch looks good.
>>>
>>> Only concern is change in the libpcap dependency. Do you know which libpcap
>>> version supports 'PCAP_TSTAMP_PRECISION_NANO'?
>>> If a user of pcap PMD updates to latest DPDK and the environment doesn't have
>>> new version of the libpcap, this change will require an environment update and
>>> this may or may not be easy to do. That is why not sure if the updates require
>>> dependency change should wait for the LTS or not.
>>>
>>> Another things is the backward compatibility, as far as I understand the pcap
>>> file recorded with nanosecond precision can be read and parsed without problem
>>> by old application that doesn't know the nanosecond precision, but can you
>>> please confirm this?
>>
>> We should do pcapng instead of doing the pcap with nano timestamp.
>> My impression is that libpcap is a dormant project at this point, and the
>> finer grain timestamp is a hack that is only in some verisions.
>> That was one of the reasons pcapng started.
> 
> Reading tv_usec as nanoseconds has been supported for years in libpcap.
> 
> For instance PCAP_TSTAMP_PRECISION_NANO was introduced in ba89e4a18e8b
> ("Make timestamps precision configurable") on May 17, 2013.

Thanks for the commit info, it looks like this support exists since
libpcap-1.5.0, and even CentOS 7 has libpcap-1.5.3-xx so looks safe to proceed.

  parent reply	other threads:[~2020-06-04 10:52 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-23 17:21 Vivien Didelot
2020-05-23 17:21 ` [dpdk-dev] [PATCH 2/2] net/pcap: add TODO for writing Tx HW timestamp Vivien Didelot
2020-05-24  1:38   ` Stephen Hemminger
2020-06-03 17:31     ` Ferruh Yigit
2020-05-24  1:39 ` [dpdk-dev] [PATCH 1/2] net/pcap: support software Tx nanosecond timestamp Stephen Hemminger
2020-06-03 17:50 ` Ferruh Yigit
2020-06-03 20:11   ` Stephen Hemminger
     [not found]     ` <20200603162652.GB13716@t480s.localdomain>
2020-06-03 21:59       ` Stephen Hemminger
2020-06-04 10:52       ` Ferruh Yigit [this message]
2020-06-04 11:16         ` Ferruh Yigit
2020-06-04 10:55     ` Ferruh Yigit

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