Re: [RFC PATCH 00/13] Ultra Ethernet driver introduction

Leon Romanovsky
2025-03-12T15:10:42Z

On Wed, Mar 12, 2025 at 04:20:08PM +0200, Nikolay Aleksandrov wrote:
> On 3/12/25 1:29 PM, Leon Romanovsky wrote:
> > On Wed, Mar 12, 2025 at 11:40:05AM +0200, Nikolay Aleksandrov wrote:
> >> On 3/8/25 8:46 PM, Leon Romanovsky wrote:
> >>> On Fri, Mar 07, 2025 at 01:01:50AM +0200, Nikolay Aleksandrov wrote:
> [snip]
> >> Also we have the ephemeral PDC connections>> that come and go as
> needed. There more such objects coming with more
> >> state, configuration and lifecycle management. That is why we added a
> >> separate netlink family to cleanly manage them without trying to fit
> >> a square peg in a round hole so to speak.
> >
> > Yeah, I saw that you are planning to use netlink to manage objects,
> > which is very questionable. It is slow, unreliable, requires sockets,
> > needs more parsing logic e.t.c
> >
> > To avoid all this overhead, RDMA uses netlink-like ioctl calls, which
> > fits better for object configurations.
> >
> > Thanks
>
> We'd definitely like to keep using netlink for control path object
> management. Also please note we're talking about genetlink family. It is
> fast and reliable enough for us, very easily extensible,
> has a nice precise object definition with policies to enforce various
> limitations, has extensive tooling (e.g. ynl), communication can be
> monitored in realtime for debugging (e.g. nlmon), has a nice human
> readable error reporting, gives the ability to easily dump large object
> groups with filters applied, YAML family definitions and so on.
> Having sockets or parsing are not issues.

Of course it is issue as netlink relies on Netlink sockets, which means
that you constantly move your configuration data instead of doing
standard to whole linux kernel pattern of allocating configuration
structs in user-space and just providing pointer to that through ioctl
call.

However, this discussion is premature and as an intro it is worth to
read this cover letter for how object management is done in RDMA
subsystem.

https://lore.kernel.org/linux-rdma/1501765627-104860-1-git-send-email-matanb@mellanox.com/

Thanks

>
> Cheers,
> Nik
>
>