[Bug 98897] Macbook pro 11,5 screen flicker when AC adapter plugged in - bugzilla-daemon

From: bugzilla-daemon@freedesktop.org
To: dri-devel@lists.freedesktop.org
Subject: [Bug 98897] Macbook pro 11,5 screen flicker when AC adapter plugged in
Date: Wed, 30 Nov 2016 20:34:56 +0000	[thread overview]
Message-ID: <bug-98897-502-IgTZYjyQV9@http.bugs.freedesktop.org/> (raw)
In-Reply-To: <bug-98897-502@http.bugs.freedesktop.org/>

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https://bugs.freedesktop.org/show_bug.cgi?id=98897

--- Comment #9 from Tom B <tom@r.je> ---
I did a bit more digging to see what the connection is with the power cable and
it seems unrelated. 

The flicker happens only when the power cable is connected AND the power mode
is performance (or balanced***see bottom of post***).

But, power_dpm_state seems to be ignored unless the power cable is plugged in.
To test this I ran unigine-heaven with default settings

power cable + battery dpm state = 4fps

power cable + performance dpm state = 8fps

no power cable  + battery dpm state = 4fps

no power cable  + performance dpm state = 4fps

So obviously the last result tells us that having the power cable unplugged
forces "battery" mode regardless of whether "performance" is set in
power_dpm_state and the power cable itself is a bit of a red herring, it's the
performance dpm state which causes the flicker and having the power cable
connected is the only way to get the gpu into performance mode.

(These numbers seem rather low for a M370X GPU since it apparently gets 35 in
windows, see
http://www.mobiletechreview.com/notebooks/15-inch-Retina-MacBook-Pro-2015.htm
I'm not sure how the radeon driver stacks up and I'm not really bothered about
that as I don't any gpu intensive work, but the performance may highlight clock
speed issues)

***** Note on "balanced". Since "balanced" always seems to cause the flicker
and high temperatures when enabled, it suggests that it's being rather
over-zealous with its clock speeds. Forcing "battery" has no noticeable impact
on performance  in desktop applications. I'm not sure how it's measured but
"balanced" would probably be better with a different threshold.

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