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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [HSW][bisected] "sna: Defer submission of the next shadow frame until halfway through" causes stuttering"
href="https://bugs.freedesktop.org/show_bug.cgi?id=107421">107421</a>
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<th>Summary</th>
<td>[HSW][bisected] "sna: Defer submission of the next shadow frame until halfway through" causes stuttering
</td>
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<th>Product</th>
<td>xorg
</td>
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<th>Version</th>
<td>unspecified
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<th>Hardware</th>
<td>x86-64 (AMD64)
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<th>OS</th>
<td>Linux (All)
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>medium
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<th>Component</th>
<td>Driver/intel
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
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<th>Reporter</th>
<td>thomas.lindroth@gmail.com
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<th>QA Contact</th>
<td>intel-gfx-bugs@lists.freedesktop.org
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<pre>Hardware: Haswell i7-4790K IGPU using all 3 connectors. All 3 monitors run at
<a href="mailto:1920x1200@59.95hz">1920x1200@59.95hz</a>
Software: kernel-4.14.59, xorg-server-1.19.5, xf86-video-intel-git
(AccelMethod=sna, TearFree=on), mesa-17.3.9, xfce-4.12 without compositing.
commit af36a4ab78cc0e2a85fa40d442bfb92df75dd217
Author: Chris Wilson <<a href="mailto:chris@chris-wilson.co.uk">chris@chris-wilson.co.uk</a>>
Date: Sun Apr 1 13:13:19 2018 +0100
sna: Defer submission of the next shadow frame until halfway through
Do not immediately post the next shadow flip on completion of the
current flips, but instead queue a timer for half way through the next
vblank so that try to we keep the additional input-output lag to less
than a frame.
After commit af36a4ab78cc0e2a85fa40d442bfb92df75dd217 I've been getting a lot
of stuttering when playing video. Both mpv and glxgears stutters. By stutter I
mean dropped and duplicated frames.
The stutter only happens when multiple heads are active. Either clone mode or
side by side. The stutter is periodic. It happens every 20 sec and last for
about 5 sec. The remaining 15 sec is smooth. My guess is that I just ended up
with those times on my system by accident. A side effect of my framerate and
how fast the framerate drifts between my monitors or something like that.
I assumed the problem was in kernel space first and while debugging I noticed
that the tracepoint i915:intel_engine_notify ring=0 fires a lot during
stuttering but not when playback is smooth. notify_ring() is part of the irq
handler so the RCS engine sends interrupts during stutter but not otherwise. I
don't know what that means. The commit before the bad commit have no periodic
stutter but the RCS engine sends interrupts almost constantly instead.
Let me know if you need any special debug output.</pre>
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