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

[Paul Emmerich <emmericp@net.in.tum.de>]

Hi,

the examples in timestamping-tests 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

On 22.10.16 12:19, Huynhtu Dang wrote:
> 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
>
>
>

-- 
Paul Emmerich
Technical University of Munich (TUM)
Department of Informatics
Chair for Network Architectures and Services