linux-kernel - Re: [RFC simple allocator v2 1/2] Create Simple Allocator module

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Date:   Wed, 15 Feb 2017 09:51:31 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Laura Abbott <labbott@...hat.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "Clark, Rob" <robdclark@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [RFC simple allocator v2 1/2] Create Simple Allocator module

2017-02-14 20:59 GMT+01:00 Laurent Pinchart <laurent.pinchart@...asonboard.com>:
> Hi Daniel,
>
> On Tuesday 14 Feb 2017 20:44:44 Daniel Vetter wrote:
>> On Tue, Feb 14, 2017 at 8:39 PM, Laurent Pinchart wrote:
>> > On Tuesday 14 Feb 2017 20:33:58 Daniel Vetter wrote:
>> >> On Mon, Feb 13, 2017 at 3:45 PM, Benjamin Gaignard wrote:
>> >>> This is the core of simple allocator module.
>> >>> It aim to offert one common ioctl to allocate specific memory.
>> >>>
>> >>> version 2:
>> >>> - rebased on 4.10-rc7
>> >>>
>> >>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
>> >>
>> >> Why not ION? It's a bit a broken record question, but if there is a
>> >> clear answer it should be in the patch&docs ...
>> >
>> > There's a bit of love & hate relationship between Linux developers and
>> > ION. The API has shortcomings, and attempts to fix the issues went
>> > nowhere. As Laura explained, starting from a blank slate (obviously
>> > keeping in mind the lessons learnt so far with ION and other similar APIs)
>> > and then adding a wrapper to expose ION on Android systems (at least as an
>> > interim measure) was thought to be a better option. I still believe it is,
>> > but we seem to lack traction. The problem has been around for so long that
>> > I feel everybody has lost hope.
>> >
>> > I don't think this is unsolvable, but we need to regain motivation. In my
>> > opinion the first step would be to define the precise extent of the
>> > problem we want to solve.
>>
>> I'm not sure anyone really tried hard enough (in the same way no one
>> tried hard enough to destage android syncpts, until last year). And
>> anything new should at least very clearly explain why ION (even with
>> the various todo items we collected at a few conferences) won't work,
>> and how exactly the new allocator is different from ION. I don't think
>> we need a full design doc (like you say, buffer allocation is hard,
>> we'll get it wrong anyway), but at least a proper comparison with the
>> existing thing. Plus explanation why we can't reuse the uabi.
>
> I've explained several of my concerns (including open questions that need
> answers) in another reply to this patch, let's discuss them there to avoid
> splitting the discussion.
>
>> Because ime when you rewrite something, you generally get one thing
>> right (the one thing that pissed you off about the old solution), plus
>> lots and lots of things that the old solution got right, wrong
>> (because it's all lost in the history).
>
> History, repeating mistakes, all that. History never repeats itself though. We
> might make similar or identical mistakes, but there's no fatality, unless we
> decide not to try before even starting :-)
>
>> ADF was probably the best example in this. KMS also took a while until all
>> the fbdev wheels have been properly reinvented (some are still the same old
>> squeaky onces as fbdev had, e.g. fbcon).
>>
>> And I don't think destaging ION is going to be hard, just a bit of
>> work (could be a nice gsoc or whatever).
>
> Oh, technically speaking, it would be pretty simple. The main issue is to
> decide whether we want to commit to the existing ION API. I don't :-)

I think that Laura have give her felling about ION when commenting the previous
version of this patchset:
https://lkml.org/lkml/2017/1/25/76

>
> --
> Regards,
>
> Laurent Pinchart