netdev - Re: [PATCH net-next v2] ipv4: fib: Replay events when registering FIB notifier

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Date:   Wed, 2 Nov 2016 15:43:29 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     Ido Schimmel <idosch@...sch.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>, mlxsw <mlxsw@...lanox.com>,
        David Ahern <dsa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        alexander.h.duyck@...el.com,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next v2] ipv4: fib: Replay events when registering
 FIB notifier

Wed, Nov 02, 2016 at 03:35:03PM CET, roopa@...ulusnetworks.com wrote:
>On 11/2/16, 6:48 AM, Jiri Pirko wrote:
>> Wed, Nov 02, 2016 at 02:29:40PM CET, roopa@...ulusnetworks.com wrote:
>>> On Wed, Nov 2, 2016 at 12:20 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>>> Wed, Nov 02, 2016 at 03:13:42AM CET, roopa@...ulusnetworks.com wrote:
>>> [snip]
>>>
>>>>> 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,
>>>> Driver (mlxsw, rocker) maintain a cache. So I'm not sure why you say
>>>> otherwise.
>>>>
>>>>
>>>>> a pull api with efficient use of rtnl will be useful for other such cases as well.
>>>> How do you imagine this "pull API" should look like?
>>>
>>> Just like you already have added fib notifiers to parallel fib netlink
>>> notifications, the pull API is  a parallel to 'netlink dump'.
>>> Is my imagination too wild  ? :)
>> Perhaps I'm slow, but I don't understand what you mean.
> 
>>>>>
>>>>> 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)
>>>> Register early? What it would resolve? I must be missing something. We
>>>> register as early as possible. But the thing is, we cannot register
>>>> in a past. And that is what this patch resolves.
>>> sure, you must be having a valid problem then. I was just curious why
>>> your driver is not up and initialized before any of the addresses or
>>> routes get configured in the system (even on a management port). Ours
>> If you unload the module and load it again for example. This is a valid
>> usecase.
>
>I see, so you are optimizing for this use case. sure it is a valid use-case but a narrow one

It is not an optimization, it's a bug fix.


>compared to the rtnl overhead the api may bring
> (note that i am not saying you should not solve it).
>
>>
>>
>>> does. But i agree there can be races and you cannot always guarantee
>>> (I was just responding to ido's comment about adding complexity for a
>>> small problem he has to solve for management routes). Our driver does
>>> a pull before it starts. This helps when we want to reset the hardware
>>> routing table state too.
>> Can you point me to you driver in the tree? I would like to see how you
>> do "the pull".
>:), you know all this... but, if i must explicitly say it, yes,  we don't have a driver in the tree and
>we don't own the hardware. My analogy here is of a netlink dump that we use heavily for the
>same scale that you will probably deploy.

You are comparing netlink kernel-user api with in kernel api. I don't
think that is comparable, at all. Therefore I asked how you imagine
"the pull" should look like, in kernel. Stating it should look like
some user api part does not help me much :(



>i do give you full credit for the hardware and the driver and switchdev support and all that!.
>
>>
>>>
>>> But, my point was, when you are defining an API, you cannot quantify
>>> the 'past' to be just the very 'close past' or 'the past is just the
>>> management routes that were added' . Tomorrow the 'past' can be the
>>> full routing table if you need to reset the hardware state.
>> Sure.
>
>This pull api was a suggestion for an efficient use of rtnl ...similar to how the netlink
>routing dump handles it. If you cannot imagine an api like that..., sure, your call.

No, that's why I'm asking, because I was under impression you can
imagine that :)