[ovs-dev] Few observations on low performance of 64 byte packet size

Luigi Rizzo rizzo at iet.unipi.it
Wed Mar 23 09:22:18 UTC 2016


On Wed, Mar 23, 2016 at 4:35 AM, <ravali.burra at wipro.com> wrote:

> Hi All,
>
> While sending 2G traffic of 64bytes size, I see a low performance for
> Phy-Phy
> setup using OVS with DPDK. I get around 1500/1500 throughput.
>
> Following are the Platform and setup details:
> NOTE: Used OVS 2.4 and DPDK2.0.0
> 1. Intel(R) Atom(TM)
> 2. I assigned 1core to vswitchd process
> 3. Bound four I350 nics to igb_uio driver assume the ports namely 1,2,3,4.
> 4. Written the flow rules in such a way that the traffic flows from 1-2
> and 3-4
> 5. Used DPDK Pktgen to pump 2G traffic of 64bytes size from port 1 and
> port 3.
> I observed the following things:
> 1.Even though 2G traffic is pumped, the rate is still 1500/1500.
>    I am really not sure why each NIC is not transmitting beyond 750Mbps
> and sometimes even less around 700Mbps.
> 2.I also see that the receive side error counters are incremented
>     in ovs-ofctl dump-ports br0 command.
>
>
​in addition to what others said:

- 1Gbit/s is slow enough that even low end processors should
  be able to do line rate with DPDK or netmap;

- you should report the packet rate not the bit rate, which is
  meaningless and depends on how it is computed;

- bit rate depends on how you count traffic. Minimum frame size
  has 60 bytes of data, 4 bytes of CRC and 160 bits of framing,
  so the actual useful bit rate is 719 Mbit/s which is close
  to the 750 you report (once again it depends on how that number
  is counted, and whether or not it includes CRC and framing)

- on each port the theoretical max is 1.488 Mpps, but from my
  experience several (lower end) Intel 1G cards are limited by
  the hardware to rates between 1.1 and 1.35 Mpps (though some
  can actually reach line rate).
  Note that a lot of cards from all manufacturers cannot do
  line rate with 64-byte packets.


cheers
luigi



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