linux-kernel - Re: [RFC PATCH] drm/ssd130x: Allocate buffer in the CRTC's .atomic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdWv_QSatDgihr8=2SXHhvp=icNxumZcZOPwT9Q_QiogNQ@mail.gmail.com>
Date:   Fri, 1 Sep 2023 10:36:17 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH] drm/ssd130x: Allocate buffer in the CRTC's
 .atomic_check() callback

Hi Maxime,

On Fri, Sep 1, 2023 at 10:22 AM Maxime Ripard <mripard@...nel.org> wrote:
> On Wed, Aug 30, 2023 at 08:25:08AM +0200, Javier Martinez Canillas wrote:
> > The commit 45b58669e532 ("drm/ssd130x: Allocate buffer in the plane's
> > .atomic_check() callback") moved the allocation of the intermediate and
> > HW buffers from the encoder's .atomic_enable callback to primary plane's
> > .atomic_check callback.
> >
> > This was suggested by Maxime Ripard because drivers aren't allowed to fail
> > after drm_atomic_helper_swap_state() has been called, and the encoder's
> > .atomic_enable happens after the new atomic state has been swapped.
> >
> > But that change caused a performance regression in very slow platforms,
> > since now the allocation happens for every plane's atomic state commit.
> > For example, Geert Uytterhoeven reports that is the case on a VexRiscV
> > softcore (RISC-V CPU implementation on an FPGA).
>
> I'd like to have numbers on that. It's a bit surprising to me that,
> given how many objects we already allocate during a commit, two small
> additional allocations affect performances so dramatically, even on a
> slow platform.

To be fair, I didn't benchmark that.  Perhaps it's just too slow due to
all these other allocations (and whatever else happens).

I just find it extremely silly to allocate a buffer over and over again,
while we know that buffer is needed for each and every display update.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds