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From: Morten Brørup <mb@smartsharesystems.com>
To: "Vivien Didelot" <vivien.didelot@gmail.com>, <dev@dpdk.org>
Cc: "Olivier Matz" <olivier.matz@6wind.com>,
	"Ferruh Yigit" <ferruh.yigit@intel.com>,
	"Patrick Keroulas" <patrick.keroulas@radio-canada.ca>
Subject: Re: [dpdk-dev] [RFC PATCH 0/3] mlx5 to PCAP capture with hardwaretimestamps
Date: Wed, 8 Jul 2020 16:34:02 +0200
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35C6110A@smartserver.smartshare.dk> (raw)
In-Reply-To: <20200625190119.265739-1-vivien.didelot@gmail.com>

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Vivien Didelot
> Sent: Thursday, June 25, 2020 9:01 PM
> 
> This series allows to capture packets from a Mellanox ConnectX-5
> interface
> into a PCAP file with support for hardware timestamps. Since libibverbs
> already provides timestamp conversion to nanoseconds for mlx5, the
> necessary
> glue is added before writing the driver's timestamps into the PCAP
> headers.

Which clock source is the nanosecond timestamps output from this function using? CLOCK_REALTIME, the NIC clock, the CPU clock, or something else?

If it is the NIC clock, I guess a simple scaling factor could be used instead, for performance reasons. The driver could expose the scaling factor (or for even better resolution: its clock frequency), e.g. through the capabilities API, so the application can cache it and convert to nanoseconds by multiplying a scaling factor and adding an offset. The application would have to handle clock drift between the NIC clock and CLOCK_REALTIME (or some other preferred reference clock source) anyway.


      parent reply	other threads:[~2020-07-08 14:34 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-25 19:01 [dpdk-dev] [RFC PATCH 0/3] mlx5 to PCAP capture with hardware timestamps Vivien Didelot
2020-06-25 19:01 ` [dpdk-dev] [RFC PATCH 1/3] net/mlx5: add timestamp-to-ns converter from libibverbs Vivien Didelot
2020-06-26  6:41   ` Olivier Matz
2020-07-07 15:23     ` PATRICK KEROULAS
2020-06-25 19:01 ` [dpdk-dev] [RFC PATCH 2/3] ethdev: add API to convert raw timestamps to nsec Vivien Didelot
2020-06-25 19:01 ` [dpdk-dev] [RFC PATCH 3/3] net/pcap: support hardware Tx timestamps Vivien Didelot
2020-06-26  6:48   ` Olivier Matz
2020-07-06 18:36     ` PATRICK KEROULAS
2020-07-07 14:47       ` Olivier Matz
2020-07-10 19:23         ` PATRICK KEROULAS
2020-06-30 14:59   ` Stephen Hemminger
2020-07-08 14:34 ` Morten Brørup [this message]

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