From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>,
"Adrien Mazarguil" <adrien.mazarguil@6wind.com>,
"Pattan, Reshma" <reshma.pattan@intel.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] mbuf changes
Date: Mon, 31 Oct 2016 11:55:21 +0100 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC359EA8EB@smartserver.smartshare.dk> (raw)
In-Reply-To: <59AF69C657FD0841A61C55336867B5B035B32000@IRSMSX103.ger.corp.intel.com>
About the mbuf timestamp (regardless of size etc.) accuracy:
We should also consider the clock source. If the NIC HW is the clock source, there will be a fixed offset from the CPU's clock, but there will also be varying drift (they have separate XTALs). And if there are multiple NICs, there will be offset and varying drift between their clocks too.
If I remember correctly, the IEEE Ethernet specifications require a clock accuracy of 100 ppm. So XTALs of this quality are probably being used in the hardware. This means that the clock drift between two NICs (or a NIC and the actual time) can be in the magnitude of 100.000 ns per second.
BTW: If you are interested in NTP, you should take a look at Poul-Henning Kamp's ntimed research: http://phk.freebsd.dk/time/index.html
Med venlig hilsen / kind regards
- Morten Brørup
next prev parent reply other threads:[~2016-10-31 10:55 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-24 15:49 Morten Brørup
2016-10-24 16:11 ` Wiles, Keith
2016-10-24 16:25 ` Bruce Richardson
2016-10-24 21:47 ` Morten Brørup
2016-10-25 8:53 ` Bruce Richardson
2016-10-25 10:02 ` Ananyev, Konstantin
2016-10-25 10:22 ` Morten Brørup
2016-10-25 13:00 ` Olivier Matz
2016-10-25 13:04 ` Ramia, Kannan Babu
2016-10-25 13:24 ` Thomas Monjalon
2016-10-25 14:32 ` Ramia, Kannan Babu
2016-10-25 14:54 ` Thomas Monjalon
2016-10-25 13:15 ` Bruce Richardson
2016-10-25 13:20 ` Thomas Monjalon
2016-10-25 9:39 ` Adrien Mazarguil
2016-10-25 10:11 ` Morten Brørup
2016-10-25 11:04 ` Adrien Mazarguil
2016-10-25 11:13 ` Bruce Richardson
2016-10-25 12:16 ` Morten Brørup
2016-10-25 12:20 ` Bruce Richardson
2016-10-25 12:33 ` Morten Brørup
2016-10-25 12:45 ` Bruce Richardson
2016-10-25 12:48 ` Olivier Matz
2016-10-25 13:13 ` Morten Brørup
2016-10-25 13:38 ` Ananyev, Konstantin
2016-10-25 14:25 ` Morten Brørup
2016-10-25 14:45 ` Olivier Matz
2016-10-28 13:34 ` Pattan, Reshma
2016-10-28 14:11 ` Morten Brørup
2016-10-28 15:25 ` Pattan, Reshma
2016-10-28 16:50 ` Adrien Mazarguil
2016-10-28 17:00 ` Richardson, Bruce
2016-10-28 20:27 ` Morten Brørup
2016-10-31 10:55 ` Morten Brørup [this message]
2016-10-31 16:05 ` Morten Brørup
2016-10-25 13:48 ` Adrien Mazarguil
2016-10-25 13:58 ` Ananyev, Konstantin
2016-10-25 11:54 ` Shreyansh Jain
2016-10-25 12:05 ` Bruce Richardson
2016-10-26 8:28 ` Alejandro Lucero
2016-10-26 9:01 ` Morten Brørup
2016-11-09 11:42 ` Alejandro Lucero
2016-11-10 9:19 ` [dpdk-dev] Fwd: " Alejandro Lucero
2016-10-25 12:49 ` [dpdk-dev] " Morten Brørup
2016-10-25 13:14 ` Olivier Matz
2016-10-25 13:18 ` Morten Brørup
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