[ovs-discuss] Throughput losses with HP Switch

Justin Pettit jpettit at ovn.org
Thu Jul 13 06:18:33 UTC 2017

I don't think this is the right forum for this question, since it doesn't seem related to OVS.  However, if I were to speculate, my guess is that the forwarding ASIC doesn't support modifying the ToS bits, so the packets are being forwarded to the management CPU to handle these packets.  You could probably get more definitive answers from an HP forum.

Good luck.


> On Jul 12, 2017, at 11:01 PM, Chaitanya Kumar <chaitanya12031 at iiitd.ac.in> wrote:
> Hi
>   We are working on a research project that involves HP OpenFlow-enabled switch (HP 3500 yl). We are facing some issues with performance particularly when operating the switch in "OpenFlow" mode. The switch is controlled via a desktop running the Ryu controller.
> The rules on the switch match packets based on the fields supported by OpenFlow. Further, the switch also modifies a certain IP header field (in this case the ToS bits) for packets that match the rules and are hence forwarded. 
> More precisely, the rules match the ToS bits of the packet and change them to a different value before forwarding them to a chosen host. 
> However, in the process, the forwarded packets achieve a throughput of no more than 700kbps, while the source and destination hosts have 100 Mbit/s Ethernet ports. 
> If we disable "OpenFlow" mode and use it as it is then we achieve a full throughput of 100Mbit/s (the Ethernet link speeds of the client and server hosts). The end-to-end throughput was measured using 
> iperf. 
> Could someone shed some light on the reason for this drastic performance degradation? (all the switch does is match packets whose ToS value is (say,) 0x28 and replaces it with 0x40 before forwarding them to the right destination)
> Also, is there an alternative switch that someone has used successfully for similar things?
> A figure showing our experiment scenario is given below, for reference.
> Thanks,
> Chaitanya
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