linux-kernel - Re: [PATCH v2 0/4] have the vt console preserve unicode characters

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Message-ID: <20180622165927.68679862@alans-desktop>
Date:   Fri, 22 Jun 2018 16:59:27 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Adam Borowski <kilobyte@...band.pl>
Cc:     Dave Mielke <Dave@...lke.cc>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] have the vt console preserve unicode characters

> The other point is a quite pointless assumption that existing scrollback is
> "optimized".  Even vgacon mostly uses software scrollback these days, as the
> amount of VGA display memory is really small.

All of our console driver code is horribly unoptimized for most of
todays hardware. Long ago I did look at what was needed but it's a
seriously non-trivial change. In particular

- Console I/O occurs under enough locks to keep fort knox safe. That
  means it's very very hard to accelerate

- The logic is plain wrong for a lot of modern video. We shouldn't be
  scrolling, we should be rendering the current backing text buffer at
  video refresh rate or similar and if the source of the updates outruns
  us it doesn't matter - we don't have to draw all the glyphs as if we
  were fast enough they would have been a blur anyway.
 
> I don't know much about console display drivers in general, though, and it
> looks like most of them are unmaintained (just noticed that sisusb for
> example hasn't seen a maintainer action for 13 years, and that person's
> domain expired in 2006).

There has been some work on them but they are not in a good state, and as
a result we have problems like these as well as the inability to nicely
support multi-console systems except in Wayland/X.

Alan