From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by dpdk.org (Postfix) with ESMTP id 24D9D1B1BD for ; Fri, 19 Jan 2018 23:53:41 +0100 (CET) Received: from cpe-2606-a000-111b-4011-eaa3-4b92-4a68-8f24.dyn6.twc.com ([2606:a000:111b:4011:eaa3:4b92:4a68:8f24] helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.63) (envelope-from ) id 1ecfXP-0005ak-I8; Fri, 19 Jan 2018 17:53:34 -0500 Date: Fri, 19 Jan 2018 17:52:59 -0500 From: Neil Horman To: Thomas Monjalon Cc: dev@dpdk.org, Matan Azrad , Bruce Richardson , "Ananyev, Konstantin" , Gaetan Rivet , "Wu, Jingjing" Message-ID: <20180119225259.GA28284@hmswarspite.think-freely.org> References: <20180118131017.GA1622@hmswarspite.think-freely.org> <1959306.0b6nHJGtEC@xps> <20180119194739.GF9519@hmswarspite.think-freely.org> <2018230.dXJnJTqQbo@xps> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2018230.dXJnJTqQbo@xps> User-Agent: Mutt/1.9.1 (2017-09-22) X-Spam-Score: -2.9 (--) X-Spam-Status: No Subject: Re: [dpdk-dev] [PATCH v2 2/6] ethdev: add port ownership X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Jan 2018 22:53:41 -0000 On Fri, Jan 19, 2018 at 09:19:18PM +0100, Thomas Monjalon wrote: Apolgies for the top post, but I'm preparing for a trip out of the country, and so may not have time to fully answer these questions until I get back (or at least until I get someplace with power and internet). If the conversation is still going at that time, I'll chime back in Neil > 19/01/2018 20:47, Neil Horman: > > On Fri, Jan 19, 2018 at 07:12:36PM +0100, Thomas Monjalon wrote: > > > 19/01/2018 18:43, Neil Horman: > > > > 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. > > > > > > Sorry, I don't understand. Please could you rephrase? > > > > > > > Sure, I'm saying the fact that you want an owner to be an object > > (library/port/process) rather than strictly an execution context > > (process/thread) doesn't preclude what I'm proposing above. You can create a > > generic version of the strcture I propose above like so: > > > > struct rte_obj_heirarchy { > > struct rte_obj_heirarchy *children; > > struct rte_obj_heirarchy *parent; > > void *owner_data; /* optional */ > > }; > > > > And embed that structure in any object you would like to give a representative > > heirarchy to, you then have a fairly simple api > > > > struct rte_obj_heirarchy *heirarchy_alloc(); > > bool heirarchy_set(struct rte_obj_heirarchy *parent, struct rte_obj_heirarcy *child) > > void heirarchy_release(struct rte_obj_heirarchy *obj) > > > > That gives you the privately held list relationship I think you are in part > > looking for (i.e. the ability for a failsafe device to iterate over the ports it > > is in control of), without the awkwardness of the ordinal priority that the > > current implementation imposes. > > What is the awkward ordinal priority? > I see you discuss it below. So let's discuss it below. > > > In summary, if what you want is ownership in the strictest sense of the word > > (i.e. mutually exclusive access, which I think makes sense), then using a lock > > and flag is really the simplest way to go. If instead what you want is a > > heirarchical relationship where you can iterate over a limited set of objects > > (the failsafe child port example), then the above is what you want. > > We want only ownership. That's why it's called ownership :) > The hierarchical relationship is private to the owner. > For instance, failsafe implements its own list of sub-devices. > So we just need to expose that the ports are already owned. > > > The soution Matan is providing does some of each of these things, but comes with > > very odd side effects > > > > It offers a level of mutual exclusion, in that only one > > object can own another at a time, but does so in a way that introduces this very > > atypical ordinality (once an ownership object is created with owner_new, any > > previously created ownership object will be denied the ability to take ownership > > of a port) > > You mean only the last owner id can take an ownership? > If yes, it looks like a bug. > Please could you show what is responsible of this effect in the patch? > > > It also offers a level of filtering (in that if you can set the ownership id of > > a given set of object to the value X, you can then iterate over them by > > iterating over all objects of that type, and filtering on their id), but it > > offers no clear in-memory relationship between parent and children (i.e. if you > > were to look at at an object in a debugger and see that it was owned by owner id > > X, it would provide you with no indicator of what object held the allocated > > ownership object assigned id X. > > I think it is wrong. There is an owner name for debug/printing purpose. > > > My proposal trades a few bytes of data in > > exchage for a global clear, definitive heirarcy relationship. And if you add an > > api call and a spinlock, you can easily graft on mutual exclusion here, by > > blocking access to objects that arent the immediate parent of a given object. > > For the hierarchical relationship, I think it is over-engineered. > For blocking access, it means you need a caller id parameter in every > functions in order to identify if the caller is the owner. > > My summary: > - you think there is a bug - needs to show > - you think about relationship needs that I don't see > - you think about access permission which would be a huge change >