Re: [dpdk-users] [dpdk-dev] What is the 'unit of timestamp' assigned to mbuf packet in DPDK?

[Harman Kalra <hkalra@marvell.com>]

On Fri, Nov 22, 2019 at 10:30:11PM +0530, Gokul Bargaje wrote:
> 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

Hi Gokul

octeontx2 also suports hardware timestamping, as soon as packet enter
the NIC queue, MAC writes the timestamp value to a memory location
(which is later read in mbuf->timestamp). Later using
'rte_eth_read_clock()' one can read the timestamp clock. Hence
"mbuf->timestamp - rte_eth_read_clock()" gives the time spent by packet
when it entered the queue to that point. As everybody suggested you can
refer rxtx_callback for more clarity. 
Octeontx2 driver also has 'rte_eth_read_clock()' eth op implemented

Thanks
Harman

> 
> 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*?
> > >
> >
> >
> >
> >
> >
> >