[dpdk-users] TimeStamping Packets Generated and Received via Pktgen Application
Paul Emmerich
emmericp at net.in.tum.de
Tue Oct 25 13:07:15 CEST 2016
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 at net.in.tum.de<mailto:emmericp at 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 at net.in.tum.de<mailto:emmericp at net.in.tum.de>
> <mailto:emmericp at 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
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