VF performance is limited by some kernel PCI setting. Update the document to explain the knowing issue and work around solution.
Signed-off-by: Qi Zhang <qi.z.zh...@intel.com> --- doc/guides/nics/i40e.rst | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index 4d3c7ca..557d83d 100644 --- a/doc/guides/nics/i40e.rst +++ b/doc/guides/nics/i40e.rst @@ -447,3 +447,27 @@ It means if APP has set the max bandwidth for that TC, it comes to no effect. It's suggested to set the strict priority mode for a TC that is latency sensitive but no consuming much bandwidth. + +VF performance is impacted by PCI extended tag setting +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To reach maximum NIC performance. PCI extended tag is required to be enabled. +DPDK I40E PF drvier will set this feature during initialization, but Kernel PF +driver does not. So when running traffic on a VF which is managed by kernel +PF driver, we saw significent NIC performance downgrade (for 64 bytes packet, +there is about 25% linerate downgrade for 25G device and about 35% for 40G +device). + +Solution: + +For kernel version >= 4.11, kernel's PCI driver will enale extended tag if it +detects that device support extended tag. So by default, this is not an issue. +When extended tag is be disabled by occasionally, to re-enable it, see below. + +For kernel version < 4.11, use setpci command to enable PCI extended flag +1) get current value of PCI configure register +setpci -s <XX:XX.X> a8.w +2) set bit 8 +value = value | 0x100 +3) set PCI configure register with new value. +setpci -s <XX:XX.X> a8.w=<value> -- 2.9.3
