Slow network speed on virtual machines hosted on RHEV/KVM when 'Solarflare Communications SFC9020' Ethernet controller is in use for the kvm bridge.

Solution Verified - Updated -

Issue

  • When a Solarflare Communications SFC9020 network card is used for giving uplink to KVM or RHEV bridge (aka: logical network) with VLAN tagging, virtual machines connected to the bridge face slow network speed.
* traffic within the same bridge (aka logical network) on the one hypervisor works fine
* traffic between bridges on the one hypervisor performs very poorly
* traffic into a virtual guest from a baremetal system performs at the speed of the external interface
* traffic out of a virtual guest to a baremetal system performs very poorly
  • Network thoughtput issue for virtual machines connected to KVM/RHEV bridge with VLAN tagging.

Environment

  • Red Hat Enterprise Linux 6.4 or earlier
  • Red Hat Enterprise Virtualization (hypervisor with RHEL 6.4 kernel or earlier)
  • Solarflare Communications Network Adaptors using sfc driver
  • Virtual bridges passing guest traffic
  • VLAN tagging

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