Re: [dpdk-dev] [PATCH v2 2/6] ethdev: add port ownership

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Jan 19, 2018 at 06:17:51PM +0100, Thomas Monjalon wrote:
> 19/01/2018 16:27, Neil Horman:
> > On Fri, Jan 19, 2018 at 03:13:47PM +0100, Thomas Monjalon wrote:
> > > 19/01/2018 14:30, Neil Horman:
> > > > So it seems like the real point of contention that we need to settle here is,
> > > > what codifies an 'owner'.  Must it be a specific execution context, or can we
> > > > define any arbitrary section of code as being an owner?  I would agrue against
> > > > the latter.
> > > 
> > > This is the first thing explained in the cover letter:
> > > "2. The port usage synchronization will be managed by the port owner."
> > > There is no intent to manage the threads synchronization for a given port.
> > > It is the responsibility of the owner (a code object) to configure its
> > > port via only one thread.
> > > It is consistent with not trying to manage threads synchronization
> > > for Rx/Tx on a given queue.
> > > 
> > > 
> > Yes, in his cover letter, and I contend that notion is an invalid design point.
> > By codifying an area of code as an 'owner', rather than an execution context,
> > you're defining the notion of heirarchy, not ownership. That is to say,
> > you want to codify the notion that there are top level ports that the
> > application might see, and some of those top level ports are parents to
> > subordinate ports, which only the parent port should access directly.  If thats
> > all you want to encode, there are far easier ways to do it:
> > 
> > struct rte_eth_shared_data {
> > 	< existing bits >
> > 	struct rte_eth_port_list {
> > 		struct rte_eth_port_list *children;
> > 		struct rte_eth_port_list *parent;
> > 	};
> > };
> > 
> > 
> > Build an api around a structure like that, so that the parent/child relationship
> > is globally clear, and this would be much easier, especially if you want to
> > continue asserting that the notion of synchronization/exclusion is an exercise
> > left to the application.
> 
> Not only Neil.
> An owner can be something else than a port.
> An owner can be an app process (multi-processes).
> An owner can be a library.
> The intent is really to solve the generic problem of which code
> is managing a port.
> 
I don't see how this precludes any part of what you just said.  Define the
rte_eth_port_list externally to the shared_data struct and allow any object you
want to allocate it, then anything you want to control a heirarchy of ports can
do so without issue, and the structure is far more clear than an opaque id that
carries subtle semantic ordering with it.

Neil