Re: [dpdk-users] Behavior of pktgen's "rate" option

["Wiles, Keith" <keith.wiles@intel.com>]

> On Mar 16, 2017, at 9:33 PM, Julien Castets <castets.j@gmail.com> wrote:
> 
> I'm benchmarking my DPDK application with pktgen and I don't understand how the
> "rate" parameter works.
> 
> Let's run pktgen:
> 
> $> pktgen -l '0-11' --master-lcore=0 -w 03:00.0 -- -f
> /home/jcastets/test.lua -m '[1].0'
> 
> (for information, my test.lua is at the bottom of this email)
> 
> Here, pktgen generates traffic with one core.
> 
> 
> If I set the pktgen "rate" to "20" and the packet size to "64", I would expect
> to generate 20% of my NIC's max speed of traffic. In my case with my 40Gbps
> NIC, I'd expect to generate 8Gbps of traffic.
> 
> And guess what, my expectations are good since with such configuration, pktgen
> generates traffic as expected: 8Gbps.
> 
> However:
> 
> * If I run pktgen with 2 cores (-m '[1-2].0' instead of -m '[1].0'), pktgen
>  generates 28Gbps.
> * If I run pktgen with 1 core, keep the "rate" at "20" but set the pktsize at
>  "128", pktgen generates 14Gbps (where I'd expect it to still generate 8Gbps).

Be careful in how you setup and change the size of a packet. Changing the size while Pktgen is running can lead to some weird performance. The problem is the packets already in flight are not changed to the new size or they are stuck on the TX done queue. The new TX flush API needs to be added to the PMDs and then in Pktgen I can flush all of the buffers back to the mempool and then alter the size of the mbuf. You did not state the version of Pktgen you are using, as DPDK 16.11 added some support for pktgen to locate and update all of the mbuf, I think that is kind of a hack on my part.


The code in Pktgen takes your rate and packet size to determine the number of packets to send at a given rate to obtain you desired rate. I thought the calculation  accounted for the number of TX cores, but maybe that is a bug. I would have expected 16Gbps in the two core case if I did not account for that config. I do not have direct access to the machine to verify the code.

Try stopping the traffic before changing any of the configs, changing the rate should work while Pktgen is sending. The problem is if the size of content needs to change the system should be halted. Also if you want to do a some more debugging, try quiting Pktgen between configurations and see if that works better. It is not what I intended on the usage of Pktgen is to quit all of the time.

I will try to have a look this weekend when I get back home.

> 
> 
> Can please anyone clarify how the rate/pktsize/cores relation works?
> 
> 
> 
> ### test.lua
> 
> pktgen.stop("all");
> pktgen.reset("all");
> pktgen.clear("all");
> 
> pktgen.src_mac("all", "start", "3c:fd:fe:a2:2c:88");
> pktgen.dst_mac("all", "start", "3c:fd:fe:a2:2b:b0");
> 
> pktgen.src_ip("all", "start", "192.168.1.1");
> pktgen.src_ip("all", "min", "0.0.0.0");
> pktgen.src_ip("all", "inc", "0.0.0.0");
> pktgen.src_ip("all", "max", "0.0.0.0");
> 
> pktgen.src_port("all", "start", 1234);
> pktgen.src_port("all", "min", 1234);
> pktgen.src_port("all", "inc", 1);
> pktgen.src_port("all", "max", 4096);
> 
> pktgen.ip_proto("all", "udp");
> 
> 
> pktgen.dst_ip("all", "start", "192.168.100.1");
> pktgen.dst_ip("all", "min", "192.168.100.1");
> pktgen.dst_ip("all", "inc", "0.0.0.1");
> pktgen.dst_ip("all", "max", "192.168.100.99");
> 
> pktgen.dst_port("all", "start", 1234);
> pktgen.dst_port("all", "min", 0);
> pktgen.dst_port("all", "inc", 0);
> pktgen.dst_port("all", "max", 0);
> 
> 
> pktgen.vlan("all", "off");
> pktgen.vlan_id("all", "start", 1024);
> pktgen.vlan_id("all", "min", 1);
> pktgen.vlan_id("all", "inc", 5);
> pktgen.vlan_id("all", "max", 3100);
> 
> pktgen.pkt_size("all", "start", 128); -- this is the parameter I'm
> trying to adjust
> pktgen.pkt_size("all", "min", 0);
> pktgen.pkt_size("all", "inc", 0);
> pktgen.pkt_size("all", "max", 0);
> 
> pktgen.set_range("all", "on");
> 
> pktgen.set("all", "count", 0); -- count 0 is forever
> pktgen.set("all", "rate", 20); -- this is the parameter I'm trying to adjust
> pktgen.start("all");
> 
> -- 
> Julien Castets

Regards,
Keith