Re: [dpdk-dev] DPDK User Space: Session onUseability and Ease of Use

[Vincent JARDIN <vincent.jardin@6wind.com>]

Thomas, John,

thanks for your notes.

Enclosed the contents of our chats,

On 13/10/2015 18:36, Mcnamara, John wrote:
> * PMD lite
>
>    - Do we need a lighter PMD model? Perhaps based on the Mellanox
>      model.
>    - Vincent suggested be could remove 90% of the code. I'll leave
>      Vincent explain this one.

benefits of 100% userland drivers:
   - no dependency on getting kernel patch upstreams first
   - it is possible to run on a latest HW even when the Linux host (or 
host OS) does not support the new NIC/boards supported by the DPDK

drawbacks of 100% userland drivers:
   - redundancy of source code (duplication into the kernel and userland)
       => more maintenance
   - DPDK PMDs are in fact outdated while kernel drivers are supporting 
latest HW (port management - optics - , latest HW revisions, managing 
firmware updates) more frequently
   - do not run when not root applications
   - cannot reuse port management tools from the kernels (ethtool, etc.)

ixgbe pmd
=========
    100% lines of userland
    must be run as root
    ~ 40K lines
    ~ kernel overlaps with 
http://dpdk.org/browse/dpdk/tree/drivers/net/ixgbe/base
    ~ mostly only 
http://dpdk.org/browse/dpdk/tree/drivers/net/ixgbe/ixgbe_rxtx[_vec].c is 
needed, other files are not needed (6k lines of code)

mlx4 pmd
========
    10% lines userland, then using kernel's ones
    could be run as a non root process
    ~ 5.2K lines of code
    ~ the rxtx.c file is http://dpdk.org/browse/dpdk/tree/drivers/net/mlx4/
    BUT using infiniband :( => should be cleand up to use bare minimum like,
     + /* Allocate protection domain. */
       http://dpdk.org/browse/dpdk/tree/drivers/net/mlx4/mlx4.c#n4828

     + Register memory regions -> ibv_reg_mr()
       http://dpdk.org/browse/dpdk/tree/drivers/net/mlx4/mlx4.c#n792

Best regards,
   Vincent