netdev - Re: [PATCH rdma-next 0/4] Introduce dynamic UAR allocation mode

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Message-ID: <20200318131450.GY3351@unreal>
Date:   Wed, 18 Mar 2020 15:14:50 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        Michael Guralnik <michaelgur@...lanox.com>,
        netdev@...r.kernel.org, Saeed Mahameed <saeedm@...lanox.com>,
        Yishai Hadas <yishaih@...lanox.com>
Subject: Re: [PATCH rdma-next 0/4] Introduce dynamic UAR allocation mode

On Wed, Mar 18, 2020 at 09:54:59AM -0300, Jason Gunthorpe wrote:
> On Wed, Mar 18, 2020 at 02:43:25PM +0200, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...lanox.com>
> >
> > From Yishai,
> >
> > This series exposes API to enable a dynamic allocation and management of a
> > UAR which now becomes to be a regular uobject.
> >
> > Moving to that mode enables allocating a UAR only upon demand and drop the
> > redundant static allocation of UARs upon context creation.
> >
> > In addition, it allows master and secondary processes that own the same command
> > FD to allocate and manage UARs according to their needs, this can’t be achieved
> > today.
> >
> > As part of this option, QP & CQ creation flows were adapted to support this
> > dynamic UAR mode once asked by user space.
> >
> > Once this mode is asked by mlx5 user space driver on a given context, it will
> > be mutual exclusive, means both the static and legacy dynamic modes for using
> > UARs will be blocked.
> >
> > The legacy modes are supported for backward compatible reasons, looking
> > forward we expect this new mode to be the default.
>
> We are starting to accumulate a lot of code that is now old-rdma-core
> only.

Agree

>
> I have been wondering if we should add something like
>
> #if CONFIG_INFINIBAND_MIN_RDMA_CORE_VERSION < 21
> #endif

>From one side it will definitely help to see old code, but from another
it will create many ifdef inside of the code with a very little chance
of testing. Also we will continue to have the same problem to decide when
we can delete this code.

>
> So we can keep track of what is actually a used code flow and what is
> now hard to test legacy code.
>
> eg this config would also disable the write interface(), turn off
> compat write interfaces as they are switched to use ioctl, etc, etc.

What about if we introduce one ifdef, let's say CONFIG_INFINIBAND_LEGACY
and put everything that will be declared as legacy to that bucket? And
once every 5 (???) years delete everything from that bucket.

>
> Jason