From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roopa Prabhu Subject: Re: [PATCH net-next v2] ipv4: fib: Replay events when registering FIB notifier Date: Tue, 01 Nov 2016 19:13:42 -0700 Message-ID: <58194BD6.5040406@cumulusnetworks.com> References: <1477948427-9189-1-git-send-email-idosch@idosch.org> <1477949046.7065.320.camel@edumazet-glaptop3.roam.corp.google.com> <20161031225737.7nfoy4ka3ydzhptq@splinter> <1478009999.7065.334.camel@edumazet-glaptop3.roam.corp.google.com> <5818B146.20209@cumulusnetworks.com> <20161101170345.pq2ewecw35mrurkp@splinter> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , netdev@vger.kernel.org, davem@davemloft.net, jiri@mellanox.com, mlxsw@mellanox.com, dsa@cumulusnetworks.com, nikolay@cumulusnetworks.com, andy@greyhouse.net, vivien.didelot@savoirfairelinux.com, andrew@lunn.ch, f.fainelli@gmail.com, alexander.h.duyck@intel.com, kuznet@ms2.inr.ac.ru, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, Ido Schimmel To: Ido Schimmel Return-path: Received: from mail-pf0-f174.google.com ([209.85.192.174]:34799 "EHLO mail-pf0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754155AbcKBCNp (ORCPT ); Tue, 1 Nov 2016 22:13:45 -0400 Received: by mail-pf0-f174.google.com with SMTP id n85so1802096pfi.1 for ; Tue, 01 Nov 2016 19:13:45 -0700 (PDT) In-Reply-To: <20161101170345.pq2ewecw35mrurkp@splinter> Sender: netdev-owner@vger.kernel.org List-ID: On 11/1/16, 10:03 AM, Ido Schimmel wrote: > Hi Roopa, > > On Tue, Nov 01, 2016 at 08:14:14AM -0700, Roopa Prabhu wrote: >> [snip] >> I have the same concern as Eric here. >> >> I understand why you need it, but can the driver request for an initial dump and that >> dump be made more efficient somehow ie not hold rtnl for the whole dump ?. >> instead of making the fib notifier registration code doing it. > We can do what we suggested in the last bi-weekly meeting, which is > still holding rtnl, but moving the hardware operation to delayed work. > This is possible because upper layers always assume operation was > successful and driver is responsible for invoking its abort mechanism in > case of failure. > >> these routing table sizes can be huge and an analogy for this in user-space: >> We do request a netlink dump of routing tables at initialization (on driver starts or resets)... >> but, existing netlink routing table dumps for that scale don't hold rtnl for the whole dump. >> The dump is split into multiple responses to the user and hence it does not starve other rtnl users. > In my reply to Eric I mentioned that when we register and unregister > from this chain the tables aren't really huge, but instead quite small. > I understand your concerns, but I don't wish to make things more > complicated than they should be only to address concerns that aren't > really realistic. I understand..but, if you are adding some core infrastructure for switchdev ..it cannot be based on the number of simple use-cases or data you have today. I won't be surprised if tomorrow other switch drivers have a case where they need to reset the hw routing table state and reprogram all routes again. Re-registering the notifier to just get the routing state of the kernel will not scale. For the long term, since the driver does not maintain a cache, a pull api with efficient use of rtnl will be useful for other such cases as well. If you don't want to get to the complexity of a new api right away because of the simple case of management interface routes you have, Can your driver register the notifier early ? (I am sure you have probably already thought about this) > > I believe current patch is quite simple and also consistent with other > notification chains in the kernel, such as the netdevice, where rtnl is > held during replay of events. > http://lxr.free-electrons.com/source/net/core/dev.c#L1535 as you know, netdev and routing scale are not the same thing. Looking at the current code for netdevices (replay and rollback on failure), a pull api (equivalent to the netlink dump api) may end up being less complex...with an ability to batch in the future.