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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Thu, 20 Jan 2022 13:13:43 +0100
Message-ID: <CAMuHMdVjv1+UNeXkCBE+80tdtLuNg=5d6N12hNLgJdaS-jxERg@mail.gmail.com>
Subject: Re: [PATCH] MAINTAINERS: Add Helge as fbdev maintainer
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Gerd Hoffmann <kraxel@redhat.com>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        Helge Deller <deller@gmx.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Sven Schnelle <svens@stackframe.org>
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Hi Daniel,

On Thu, Jan 20, 2022 at 12:33 PM Daniel Vetter <daniel@ffwll.ch> wrote:
> On Thu, Jan 20, 2022 at 10:06 AM Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
> > On Thu, Jan 20, 2022 at 4:29 AM Gerd Hoffmann <kraxel@redhat.com> wrote:
> > > On Tue, Jan 18, 2022 at 10:33:23AM +0200, Pekka Paalanen wrote:
> > > > On Mon, 17 Jan 2022 19:47:39 +0100
> > > > Sven Schnelle <svens@stackframe.org> wrote:
> > > > > I also tested the speed on my Thinkpad X1 with Intel graphics, and there
> > > > > a dmesg with 919 lines one the text console took about 2s to display. In
> > > > > x11, i measure 22ms. This might be unfair because encoding might be
> > > > > different, but i cannot confirm the 'memcpy' is faster than hardware
> > > > > blitting' point. I think if that would be the case, no-one would care
> > > > > about 2D acceleration.
> > > >
> > > > I think that is an extremely unfair comparison, because a graphical
> > > > terminal app is not going to render every line of text streamed to it.
> > > > It probably renders only the final view alone if you simply run
> > > > 'dmesg', skipping the first 800-900 lines completely.
> > >
> > > Probably more like "render on every vblank", but yes, unlike fbcon it
> > > surely wouldn't render every single character sent to the terminal.
> > >
> > > Also acceleration on modern hardware is more like "compose window
> > > content using the 3d engine" than "use 2d blitter to scroll the window".
> > >
> > > > Maybe fbcon should do the same when presented with a flood of text,
> > > > but I don't know how or why it works like it works.
> > >
> > > fbcon could do the same, i.e. render to fbdev in a 60Hz timer instead of
> > > doing it synchronously.
> >
> > Hopefully only the parts of the screen which need a redraw?
> >
> > Not all displays can be updated that fast. For a "modern" example, see
> > https://patchwork.freedesktop.org/series/93070/.
>
> drm does damage tracking throughout the stack, e.g.
>
> https://dri.freedesktop.org/docs/drm/gpu/drm-kms.html#damage-tracking-properties
>
> And unlike fbdev, it's explicit (so less overhead since userspace
> generally knows what it's drawn) and doesn't rely on page fault
> intercepting and fun stuff like that.

My reply was to a paragraph about rendering text by fbcon, not about
userspace rendering graphics.

> Like do people actually know what drm can and cannot do, or would that
> take out all the fun?

;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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