Re: [dpdk-dev] [PATCH] doc: announce ixgbe MTU setting limitation

["Mcnamara, John" <john.mcnamara@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Wenzhuo Lu
> Sent: Tuesday, February 7, 2017 6:23 AM
> To: dev@dpdk.org
> Cc: Lu, Wenzhuo <wenzhuo.lu@intel.com>
> Subject: [dpdk-dev] [PATCH] doc: announce ixgbe MTU setting limitation
> 
> Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
> ---
>  doc/guides/nics/ixgbe.rst | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/guides/nics/ixgbe.rst b/doc/guides/nics/ixgbe.rst index
> 3b6851b..1f7d6b3 100644
> --- a/doc/guides/nics/ixgbe.rst
> +++ b/doc/guides/nics/ixgbe.rst
> @@ -185,8 +185,11 @@ As in the case of l3fwd, set configure
> port_conf.rxmode.hw_ip_checksum=0 to enab  In addition, for improved
> performance, use -bsz "(32,32),(64,64),(32,32)" in load_balancer to avoid
> using the default burst size of 144.
> 
> 
> +Limitations or Known issues
> +---------------------------
> +
>  Malicious Driver Detection not Supported
> -----------------------------------------
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>  The Intel x550 series NICs support a feature called MDD (Malicious
> Driver Detection) which checks the behavior of the VF driver.
> @@ -207,7 +210,7 @@ it by default.)
> 
> 
>  Statistics
> -----------
> +~~~~~~~~~~
> 
>  The statistics of ixgbe hardware must be polled regularly in order for it
> to  remain consistent. Running a DPDK application without polling the
> statistics will @@ -230,6 +233,15 @@ be calculated as follows:
> 
>  In order to ensure valid results, it is recommended to poll every 4
> minutes.
> 
> +MTU setting
> +~~~~~~~~~~~
> +
> +Although user can set MTU separately on PF and VF ports, ixgbe only
> +supports one global MTU per physical port.
> +So when user sets different MTUs on PF and VF ports in one physical
> +port, the real MTU for all these PF and VF ports is the biggest one.
> +This behavior is leveraged from kernel driver.
> +

Would be slightly better as:

Although the user can set the MTU separately on PF and VF ports, the ixgbe
NIC only supports one global MTU per physical port.
So when the user sets different MTUs on PF and VF ports in one physical 
port, the real MTU for all these PF and VF ports is the largest value set.
This behavior is based on the kernel driver behavior.