X11 Accel work-around for intel(4) systems

[nob...@net.bsd]

Thought I'd post this as a kind of memory dump..

Was attempting to improve X11 performance on a old 32bit HP Slimline
with Intel on-board itegrated graphics that uses DVMT to shuffle system
memory to graphics as needed. This saves the manufacture some money
but possibly is a source of instability as the system will experience
frequent pauses during moments of higher load.

Anyway.. NetBSD apparently has a very old Linux port of DRM which results
in GPU hangs if enabled on this system. If acceleration and DRI are
disabled the system is stable but very slow.

The partial solution was to create a xorg.conf file under /etc/X11 and
add the following tweaks to the main "Device" section:

Option Accel "True"
Option AccelMethod "BLT"
Option DRI "False"

The "BLT" option (Block Litigated Transfer) seems to be the deciding
factor between having a system that still occasionally hiccups but
recovers vs a system that regularly experiences garbled display, loss
of pointer cursor or full on X11 crash that lands the user back at the
xdm login screen.

The intel(4) manpage says the BLT option tells the system to "..disable
render acceleration and only use the BLT engine". Not sure what the BLT
engine is as not much comes up in web search results but I'm guessing
it's still part of the SNA acceleration scheme and selecting "BLT"
results in a crippled "SNA" (Sandybridge New Acceleration); certainly
there is no advanced 3D acceleration going on.

Ultimately the NetBSD folks need to freshen their DRM stuff so DRI can
be enabled. Chatting with some NetBSD developers suggests this may not
be a high priority so until then work-arounds as described are the only
option.

ref:
- intel(4) manpage
- Intel HD Graphics/BLT Engine:
https://wiki.osdev.org/index.php?title=Intel_HD_Graphics&oldid=24565"

[Aelius Gallus]

nob...@net.bsd wrote:
> Thought I'd post this as a kind of memory dump..
>
> Was attempting to improve X11 performance on a old 32bit HP Slimline

..
..
..

> - intel(4) manpage
> - Intel HD Graphics/BLT Engine:
> https://wiki.osdev.org/index.php?title=Intel_HD_Graphics&oldid=24565"

Wow, I hope you, and others, will continue sharing their thoughts on this
newsgroup as it has hardly any traffic. The stuff you wrote is above my head
but somebody could find it useful.

[Paolo Vincenzo Olivo]

Sul meriggio di 020821 16:21,
nob...@net.bsd <nob...@net.bsd> enarrava tali parole:

>
> Ultimately the NetBSD folks need to freshen their DRM stuff so DRI can
> be enabled. Chatting with some NetBSD developers suggests this may not
> be a high priority so until then work-arounds as described are the only
> option.
>

As far as I can tell the graphics stack update is on on the tasklist for
-10 RELEASE, listed among "Ongoing projects and unmerged branches"; see:
https://wiki.netbsd.org/releng/netbsd-10/

Nia Alarie recently told on UnitedBSD that Riastradh has been syncing
NetBSD's graphics drivers with the DRM/KMS stack in Linux 5.6. This will
bring support for a large amount of newer hardware, as well as support
for GLAMOR, a new acceleration mode in the X Window System. The newer
shims for Linux kernel interfaces should also make future GPU driver
updates much easier, resulting in less of a lag before newer GPUs are
supported in NetBSD.

The -9.* stack is indeed much older if compared to that one, being still
stuck at 4.11, making it tediosuly hard to run NetBSD on anything above
Broadwell. Hopefully, it will make it into -10.*

If you're interested in testing the new code (still pretty much
experimental), clone the repository from Riastradh's GitHub and build a
kernel (remember to back up the known-working one):

git clone https://github.com/riastradh/netbsd-src
cd netbsd-src
git checkout reredrm56

(follow the standard instructions for building a kernel)
Please report any panics to the GitHub repository.

With Intel GPUs, the modesetting Xorg display driver must be used
currently, so you'll need to explicitly set it inside inside
/etc/X11/xorg.conf or a partial /etc/X11/xorg.conf.d/99-intel.conf
configuration file:

Section "Device"
Identifier "Card0"
Driver "modesetting"
EndSection


Personally, I'm looking forward to testing this on a Nvidia GTX 1060,
which my workstation is equipped with; this had been substantially holding
me back from installing NetBSD on it, as the nouveau(4) implementation
from Linux 4.11, dated early 2017, would support up to GTX 9xx only.

If you happen to give this a try, any feedback is welcome. As a desktop
user, I'm as much interested as you.

Regards
--
Paolo Vincenzo Olivo ~ sehnsucht.multics.org
SDF Public Access UNIX System - https://sdf.org
PGP fingerprint = 39F1 9E55 77AF 6BF3 005 B181 8F2A 9A4D 9001 2186

[sehnsucht]

Replying to this thread to notify that the drm update was merged
to HEAD's main branch in December. The current stack is in par with
Linux 5.6. You can test it by fetching a -current kernel nightly build
from nycdn.netbsd.org.

--
“Hell is empty and all the devils are here.„