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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Roopa Prabhu , Nikolay Aleksandrov , Linus =?utf-8?Q?L=C3=BCssing?= , linux-kernel@vger.kernel.org, bridge@lists.linux.dev Subject: Re: [PATCH RFC net-next 07/10] net: dsa: mv88e6xxx: Track bridge mdb objects Message-ID: <20240430005949.44lcegwhmcetpddm@skbuf> References: <20240402001137.2980589-1-Joseph.Huang@garmin.com> <20240402001137.2980589-8-Joseph.Huang@garmin.com> <20240402122343.a7o5narxsctrkaoo@skbuf> <20240405110745.si4gc567jt5gwpbr@skbuf> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Apr 29, 2024 at 06:07:25PM -0400, Joseph Huang wrote: > Something like this (some layers omitted for brevity)? > > +br_iterator > | for each mdb > | _br_switchdev_mdb_notify > rtnl_lock | without F_DEFER flag > | | | > +switchdev_port_attr_set_deferred | +switchdev_port_obj_notify > | | | > +dsa_port_mrouter | +dsa_user_port_obj_a/d > | | | > +mv88e6xxx_port_mrouter----------+ +mv88e6xxx_port_obj_a/d > | > +--------------------------------------+ > | > rtnl_unlock At a _very_ superficial glance, I don't think you are properly accounting for the fact that even with rtnl_lock() held, there are still SWITCHDEV_OBJ_ID_PORT_MDB events which may be pending on the switchdev chain. Without a switchdev_deferred_process() flush call, you won't be getting rid of them, so when you rtnl_unlock(), they will still run. Even worse, holding rtnl_lock() will not stop the bridge multicast layer from modifying its br->mdb_list; only br->multicast_lock will. So you may be better off also acquiring br->multicast_lock, and notifying the MDB entries to the switchdev chain _with_the F_DEFER flag. > Note that on the system I tested, each register read/write takes about 100us > to complete. For 100's of mdb groups, this would mean that we will be > holding rtnl lock for 10's of ms. I don't know if it's considered too long. Not sure how this is going to be any better if the iteration over MDB entries is done 100% in the driver, though - since its hook, dsa_port_mrouter(), runs entirely under rtnl_lock(). Anyway, with the SWITCHDEV_F_DEFER flag, maybe the mdb object notifications can be made to run by switchdev only a few at a time, to give the network stack time to do other things as well.