netdev - Re: [patch net-next v2 10/11] mlxsw: spectrum_router: Request a dump of FIB tables during init

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Message-Id: <1479916800.4019894.797128001.743EBB6A@webmail.messagingengine.com>
Date:   Wed, 23 Nov 2016 17:00:00 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, idosch@...lanox.com, eladr@...lanox.com,
        yotamg@...lanox.com, nogahf@...lanox.com, arkadis@...lanox.com,
        ogerlitz@...lanox.com, roopa@...ulusnetworks.com,
        dsa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        andy@...yhouse.net, vivien.didelot@...oirfairelinux.com,
        andrew@...n.ch, f.fainelli@...il.com, alexander.h.duyck@...el.com,
        kaber@...sh.net
Subject: Re: [patch net-next v2 10/11] mlxsw: spectrum_router: Request a dump of
 FIB tables during init

On Wed, Nov 23, 2016, at 15:48, Jiri Pirko wrote:
> From: Ido Schimmel <idosch@...lanox.com>
> 
> Make sure the device has a complete view of the FIB tables by invoking
> their dump during module init.
> 
> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
> ---
>  drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 16
>  ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> index 14bed1d..36a71d2 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> @@ -2027,6 +2027,21 @@ static int mlxsw_sp_router_fib_event(struct
> notifier_block *nb,
>  	return NOTIFY_DONE;
>  }
>  
> +static void mlxsw_sp_router_fib_dump(struct mlxsw_sp *mlxsw_sp)
> +{
> +       while (!fib_notifier_dump(&mlxsw_sp->fib_nb)) {
> +               /* Flush pending FIB notifications and then flush the
> +                * device's table before requesting another dump. Do
> +                * that with RTNL held, as FIB notification block is
> +                * already registered.
> +                */
> +               mlxsw_core_flush_owq();
> +               rtnl_lock();
> +               mlxsw_sp_router_fib_flush(mlxsw_sp);
> +               rtnl_unlock();
> +       }
> +}

I think it is fine to use this kind of synchronization.

But I think that this part of the logic still belongs into the core
kernel. I still think it could happen that we will loop here
indefinitely because of a lot of routing updates and as such would need
to abort this loop after a number of tries.

I would like that the kernel has one function to do this decision
instead of later patching all users of this API. Do you think it is
worth it?

Bye,
Hannes