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From: Tom Barbette <barbette@kth.se>
To: Gokul Bargaje <gokulbargaje.182009@nitk.edu.in>,
	Ferruh Yigit <ferruh.yigit@intel.com>
Cc: dev@dpdk.org, users@dpdk.org
Subject: Re: [dpdk-dev] [dpdk-users] What is the 'unit of timestamp' assigned to mbuf packet in DPDK?
Date: Wed, 27 Nov 2019 15:49:37 +0100
Message-ID: <96ea0210-3a6f-9f77-8924-6e14df5785b4@kth.se> (raw)
In-Reply-To: <CAH1-=xh_ngR-2r2gt+e_66QRN4Ec7NbXoXqW2tQXf9Vx7tTi=w@mail.gmail.com>

Hi Gokul,

As Setphen said, only Mellanox sets the hardware timestamp.

If you have a Mellanox card, you can actually follow the example given 
in the rxtx_callback sample application that precisely gives the number 
of CPU cycles a packet spent into the queue.


Tom

Le 22/11/2019 à 18:00, Gokul Bargaje a écrit :
> Thank you for the clarification. But I am still unable to understand how
> exactly timestamp is calculated before assigning to a timestamp field.
> Could you please tell me the steps to calculate the timestamp in DPDK?
> 
> I have to implement the PIE AQM algorithm in DPDK and for that, I need to
> calculate the total time spent by the packet waiting in queue (i.e. the
> difference between enqueue time and dequeue time).
> 
> Thanks,
> Gokul
> 
> On Fri, Nov 22, 2019 at 8:18 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> 
>> On 11/18/2019 2:29 PM, Gokul Bargaje wrote:
>>> Hi,
>>>
>>> The timestamp assigned to packet at the time of enqueue (value of
>> timestamp
>>> field in mbuf), is it in milliseconds or microseconds or in cpu cycles?
>>
>> The unit is not defined [1]. 'rte_eth_read_clock()' was added [2] to help
>> converting it to time when it is clock counter.
>>
>> [1]
>> 918ae9dc775e ("mbuf: add a timestamp field")
>>
>> [2]
>> 5e741377657c ("ethdev: add API to read device clock")
>>
>>>
>>> How this timestamp is calculated? Is it calculated using the
>> *rte_cycles.h*?
>>>
>>
>>
>>
>>
>>
>>

  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-18 14:29 [dpdk-dev] " Gokul Bargaje
2019-11-22 14:48 ` [dpdk-dev] [dpdk-users] " Ferruh Yigit
2019-11-22 17:00   ` Gokul Bargaje
2019-11-22 17:05     ` Stephen Hemminger
2019-11-27 14:49     ` Tom Barbette [this message]
2019-11-28  8:28     ` Harman Kalra
2019-11-25 10:56 ` Archit Pandey

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