[Intel-gfx] [PATCH v5 00/12] Enable GPU switching on pre-retina?MacBook Pro

Lukas Wunner lukas at wunner.de
Tue Mar 15 17:54:36 UTC 2016

Hi Alex,

On Sat, Mar 05, 2016 at 01:10:56PM -0500, Alex Deucher wrote:
> Is there any reason to make use of the mux?

Performance (lower latency => no need for framebuffer writes over PCIe),
improved battery life (no need to use 2 GPUs simultaneously).

Technically you can't just ignore that the mux is there on the MBP
because the kernel has no control over the GPU used on boot.
(It's determined by EFI).

> > I've heard that the AMD GPU is picky about external monitors and
> > doesn't recognize them unless they're plugged in at exactly the
> > right moment, so you may need to retry a couple of times until it
> > works.
> Are talking about some issue specific to these muxed apple systems or
> in general?

Feedback I got from William Brown of Red Hat who tested the GPU switching
patches on an MBP8,2 and reported that (independently of the patches),
a display connected with an original Apple DP-to-DVI adapter would only
be recognized if plugged in at exactly the right moment and in the correct
order (first adapter, then display). However it doesn't seem to work
better on OS X.

> If you are having issues, please file a bug.

I'm not having issues so can't file a bug. Besides, filing a bug is no
guarantee that things get fixed. He had opened a bug for GPU switching
3 years ago (https://bugs.freedesktop.org/show_bug.cgi?id=61115) and
nobody did a thing. Obviously whether something gets fixed is a function
of the perceived importance by maintainers, unless a volunteer comes
along and does the dirty work.

Best regards,


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