Re: [dpdk-users] TimeStamping Packets Generated and Received via Pktgen Application

[Ajinkya D Kadam <ajinkya.kadam@nyu.edu>]

Hi Paul,

If I am not wrong this [1] script enables only timestamps for PTP or UDP
packets. Is this similar functionality available for TCP packets ?

I am generating multiple TCP flows and I just want to time-stamp first
packet of each flow. Is this possible using the NICs hardware time-stamping
capability ?


[1] : https://github.com/libmoon/libmoon/blob/b5f6c2cac42c02db64073b57dd8ca8
2692d3858c/examples/hardware-timestamping.lua

On Tue, Oct 25, 2016 at 6:57 AM, Paul Emmerich <emmericp@net.in.tum.de>
wrote:

> Hi,
>
> the examples in "timestamping-tests.lua" are only meant as a demonstration
> of the different timestamping capabilities (and/or as a starting point for
> a custom script).
>
> In your case, you could use a device counter to print the whole throughput
> of the device. You can use the default stats task to do that by adding the
> following call in the master task:
>
>         stats.startStatsTask({rxDev, txDev})
>
> I'll also add the call to the example script in the repository later today
> as having this is probably a good idea :)
>
> Paul
>
> > Am 22.10.2016 um 12:19 schrieb Huynhtu Dang <huynh.tu.dang@usi.ch>:
> >
> > Hello Emmerich,
> >
> > MoonGen is really helpful in measuring performance of network devices.
> > I wonder if we could get some information about packet loss
> > while running timestamps-software.lua?
> >
> > Thanks,
> > Tu
> >
> > On Oct 17, 2016, at 12:41 PM, Paul Emmerich <emmericp@net.in.tum.de<
> mailto:emmericp@net.in.tum.de>> wrote:
> >
> > Hi,
> >
> > Ajinkya D Kadam:
> > I was reading through your paper and I think this tool will be much more
> > helpful to me. Btw I am using quad X710 and dual X520 NICs.
> > Is this [1] the right code to look at if i want to see how you have
> > achieved hardware based time stamping ?
> >
> > Yes, run this example script with two directly connected ports for a
> simple demo and test of your hardware's capabilities. It will work with
> both of your NICs.
> >
> > In addition, I want to confirm my understanding of why MoonGen is better
> > than PktGen in time stamping context.
> > PktGen reads the value of rdtsc which it then appends to packet, this
> > adds more delay and hence the precision is bad.
> >
> > Software timestamping by writing the TSC to the packet is also supported
> (but the API is less nice, see issue #153):
> >
> > See examples/timestamping-tests/timestamps-software.lua for an example.
> >
> > The main problem is that there is unpredictable jitter from the NIC and
> PCIe transfer and other random errors. Especially if you are running this
> at higher packet rates.
> > This leads to the 200-300ns random error that I've previously mentioned.
> >
> >
> > In case of MoonGen how does this work ? I am not sure. Could you please
> > elaborate ?
> >
> > MoonGen enables the hardware timestamping feature of the NIC and uses
> it. The NIC will store the timestamp in a register which needs to be read
> before another packet can be timestamped, this limits the throughput of
> timestamped packets. However, I've found that you rarely need to timestamp
> *all* packets in a packet generator. You'll have to use software
> timestamping if you really need that.
> >
> >
> > Paul
> >
> >
> > Thanks,
> > Ajinkya
> >
> >
> > [1] https://github.com/libmoon/libmoon/blob/
> b5f6c2cac42c02db64073b57dd8ca82692d3858c/examples/hardware-
> timestamping.lua
> >
> > ᐧ
> >
> > On Sun, Oct 16, 2016 at 6:55 PM, Paul Emmerich <emmericp@net.in.tum.de<
> mailto:emmericp@net.in.tum.de>
> > <mailto:emmericp@net.in.tum.de>> wrote:
> >
> >   Hi,
> >
> >
> >   Ajinkya D Kadam:
> >
> >       If yes I would like to modify the pktgen code so that each
> >       transmitting and
> >       received packet is timestamped.  Right now I am exploring the
> >       example
> >       applications  like rxtx_callbacks which timestamps packets in
> >       DPDK, Is this
> >       the right direction to go ?
> >
> >
> >   Check out my packet generator MoonGen
> >   https://github.com/emmericp/MoonGen
> >   <https://github.com/emmericp/MoonGen>
> >
> >   It uses the hardware timestamping features (PTP) to do latency
> >   measurements in the nanosecond-range.
> >
> >   However, if you will run into hardware limitations if you want to
> >   timestamp *all* packets. This is sometimes supported on RX (e.g.,
> >   i310, X550) but I don't know a NIC that supports this on TX.
> >
> >   As for the precision that is achievable: ~10ns (depending on the
> >   NIC) with hardware support. Software timestamping will typically
> >   result in a standard deviation of 200-300ns under load and there
> >   will be huge outliers.
> >
> >
> >    Paul
>
>