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Re: Funky Display Output:

On Tue, 30 Apr 2019, Ron Georgia wrote:

> When I switched to using modesetting the tearing issue went away;
> however the display was a little grainy and there was a lot of "lag"
> in the video when doing things like moving a window (like when I used
> to use Window 3.1.1 on my 286 6MHz beast of a machine). I changed the
> driver to intel and, as stated before, set Option "TearFree" to "true"
> and "AccelMethod" to "sna"

I mention "modesetting" because that is the only thing that works for
the machines I have (i82G41TY-, i82Q45-, i82946GZ-based).  Using 'Driver
"intel"' with 'Option "TearFree" "true"' and 'Option "AccelMethod" "SNA"'
does not produce a usable display on these machines.

> I do not see any performance hits with those settings. I need to dig
> into what those really do, since I found those settings on the web,
> maybe Arch Linux or something. As a refresher here are some snippets
> of my dmesg, in case that will help someone else with similar hardware.

I do see some performance impact, although in my case that could partly
be due to running over NFS (machines have netbsd-8 only on local disk).
If the server is busy, things lag.

I am seeing the same kind of error messages logged to the console.  I
thought there was a pattern to them, but was just contradicted as I
pasted this:

[ 162875.7671473] kern error: [drm:(/x/current/src/sys/external/bsd/drm2/dist/drm/i915/intel_fifo_underrun.c:363)intel_cpu_fifo_underrun_irq_handler] *ERROR* CPU pipe A FIFO underrun
[ 163245.8965324] kern error: [drm:(/x/current/src/sys/external/bsd/drm2/dist/drm/i915/intel_sprite.c:132)intel_pipe_update_start] *ERROR* Potential atomic update failure on pipe A: -35

Still, seems to be usually one of the first followed by two or more of
the second, although not necessarily.  Sometimes several of the first
will occur before the second.

So far, the only machines I have that do not have a problem using 'Driver
"intel"' use actual i82915 devices or i82810e devices.  For those,
setting 'Option "TearFree" "false"' has no adverse effect and saves a
performance penalty.

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