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List: kwin
Subject: Re: Review Request 109783: split hasWaitSync to blocksForRetrace and syncsToVBlank
From: Thomas_Lübking <thomas.luebking () gmail ! com>
Date: 2013-03-31 17:51:50
Message-ID: 20130331175150.3641.74423 () vidsolbach ! de
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> On None, Thomas Lübking wrote:
> > kwin/glxbackend.cpp, line 115
> > <http://git.reviewboard.kde.org/r/109783/diff/1/?file=125912#file125912line115>
> >
> > Currently hardcoded.
> > We really should find a way to auto-determine this, no user can possible figure \
> > that himself.
>
> Ralf Jung wrote:
> > no user can possible figure that himself
> That's true. However, I wonder how many users will even need a setting of "true" \
> here. Maybe I can convince my father to install a Kubuntu test installation on his \
> laptop with an AMD card, so I can check how the AMD drivers behave. What could be \
> done (in a different patch, preferably ;-) is calling SwapBufers three times \
> immediately after each other. This should take at least 32ms in a double-buffered \
> blocking scenario, while it should never take more than 16ms in a triple-buffered \
> "block only if two frames are already queued" scenario (assuming 60Hz). However, \
> IMHO this should be done on first startup only (and/or if the GPU setup changes - \
> if KWin can detect that) as it will delay KWin starting and might cause flicker.
> calling SwapBufers three times immediately after each other. This should take at \
> least 32ms in a double-buffered blocking scenario
Yes.
> while it should never take more than 16ms in a triple-buffered "block only if two \
> frames are already queued" scenario
I fear it's more like "block only if one frame is queued" for triple buffering \
(you're waiting for the frontbuffer to free the backbuffer - if you queue rather than \
discard frames you'll only have the first out of two subsequent swaps for free) - so \
a) a double swap is a sufficient indicator, but b) you'll then wait for (x)ms + 16ms \
in the double buffering and (16 - y)ms in the triple buffering case
- x is the blocking time until the next retrace, the 2nd 16ms you'll wait for sure
- on blocking triple buffering the first swap comes for free and then you'll have to \
wait until the next restrace (<= 16ms)
So the test would be to swap twice. If that takes < 15ms you've triple buffering and \
if it takes > 17ms you've double buffering (given there's sufficient CPU time for \
that thread in general) If you end up between 15 & 17 ms there could be either and \
you got to retest (by knowing that a blocking swap and thus retrace just occured - so \
sleeping 16+8ms should kick you into a more expressive condition)
I'm not yet sure where to put that (apparently not init and if we wanted to cache it, \
we'd have to check whether the X server is new - until some driver permits changing \
that at runtime)
Another option was to start with the assumption of triple buffering and measure swaps \
online - if then there's a "significant" amount of swaps that take "significantly" \
more than no time, we can pretty much assume that this is a blocking swap and change \
the state at runtime.
- Thomas
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
http://git.reviewboard.kde.org/r/109783/#review30049
-----------------------------------------------------------
On March 28, 2013, 10:32 p.m., Thomas Lübking wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/109783/
> -----------------------------------------------------------
>
> (Updated March 28, 2013, 10:32 p.m.)
>
>
> Review request for kwin, Martin Gräßlin and Ralf Jung.
>
>
> Description
> -------
>
> ... for that is not the same (though atm. syncsToVBlank is only used to determine \
> the fps interval - other usage pot. for supportInfo etc.)
> Also "hasWaitSync" is an implementation detail of GLX - EGL doesn't have it.
>
>
> Diffs
> -----
>
> kwin/composite.cpp ee885dc
> kwin/eglonxbackend.cpp ecb6e0a
> kwin/glxbackend.h 49b897e
> kwin/glxbackend.cpp c68bcee
> kwin/scene.h 5d49c40
> kwin/scene.cpp 939f000
> kwin/scene_opengl.h 409ec3d
> kwin/scene_opengl.cpp 3343164
>
> Diff: http://git.reviewboard.kde.org/r/109783/diff/
>
>
> Testing
> -------
>
> Compiles and runs. Is part of https://git.reviewboard.kde.org/r/109086/ and has \
> been used for pretty long here now.
>
> Thanks,
>
> Thomas Lübking
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="http://git.reviewboard.kde.org/r/109783/">http://git.reviewboard.kde.org/r/109783/</a>
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<br />
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On , <b>Thomas Lübking</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;">
<table width="100%" border="0" bgcolor="white" style="border: 1px solid #C0C0C0; \
border-collapse: collapse; margin: 2px padding: 2px;"> <thead>
<tr>
<th colspan="4" bgcolor="#F0F0F0" style="border-bottom: 1px solid #C0C0C0; \
font-size: 9pt; padding: 4px 8px; text-align: left;"> <a \
href="http://git.reviewboard.kde.org/r/109783/diff/1/?file=125912#file125912line115" \
style="color: black; font-weight: bold; text-decoration: \
underline;">kwin/glxbackend.cpp</a> <span style="font-weight: normal;">
(Diff revision 1)
</span>
</th>
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</thead>
<tbody style="background-color: #e4d9cb; padding: 4px 8px; text-align: center;">
<tr>
<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">void \
GlxBackend::init()</pre></td>
</tr>
</tbody>
<tbody>
<tr>
<th bgcolor="#b1ebb0" style="border-right: 1px solid #C0C0C0;" \
align="right"><font size="2"></font></th> <td bgcolor="#c5ffc4" width="50%"><pre \
style="font-size: 8pt; line-height: 140%; margin: 0; "></pre></td> <th \
bgcolor="#b1ebb0" style="border-left: 1px solid #C0C0C0; border-right: 1px solid \
#C0C0C0;" align="right"><font size="2">106</font></th> <td bgcolor="#c5ffc4" \
width="50%"><pre style="font-size: 8pt; line-height: 140%; margin: 0; "> \
<span class="n">setBlocksForRetrace</span><span class="p">(</span><span \
class="nb">false</span><span class="p">);</span></pre></td> </tr>
</tbody>
</table>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Currently hardcoded. We \
really should find a way to auto-determine this, no user can possible figure that \
himself.</pre> </blockquote>
<p>On March 29th, 2013, 10:07 a.m. UTC, <b>Ralf Jung</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">> no user can \
possible figure that himself That's true. However, I wonder how many users will \
even need a setting of "true" here. Maybe I can convince my father to \
install a Kubuntu test installation on his laptop with an AMD card, so I can check \
how the AMD drivers behave. What could be done (in a different patch, preferably ;-) \
is calling SwapBufers three times immediately after each other. This should take at \
least 32ms in a double-buffered blocking scenario, while it should never take more \
than 16ms in a triple-buffered "block only if two frames are already \
queued" scenario (assuming 60Hz). However, IMHO this should be done on first \
startup only (and/or if the GPU setup changes - if KWin can detect that) as it will \
delay KWin starting and might cause flicker. </pre>
</blockquote>
</blockquote>
<pre style="margin-left: 1em; white-space: pre-wrap; white-space: -moz-pre-wrap; \
white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">> \
calling SwapBufers three times immediately after each other. This should take at \
least 32ms in a double-buffered blocking scenario Yes.
> while it should never take more than 16ms in a triple-buffered "block only \
if two frames are already queued" scenario I fear it's more like "block \
only if one frame is queued" for triple buffering (you're waiting for the \
frontbuffer to free the backbuffer - if you queue rather than discard frames \
you'll only have the first out of two subsequent swaps for free) - so a) a double \
swap is a sufficient indicator, but b) you'll then wait for (x)ms + 16ms in the \
double buffering and (16 - y)ms in the triple buffering case
- x is the blocking time until the next retrace, the 2nd 16ms you'll wait for \
sure
- on blocking triple buffering the first swap comes for free and then you'll have \
to wait until the next restrace (<= 16ms)
So the test would be to swap twice. If that takes < 15ms you've triple \
buffering and if it takes > 17ms you've double buffering (given there's \
sufficient CPU time for that thread in general) If you end up between 15 & 17 ms \
there could be either and you got to retest (by knowing that a blocking swap and thus \
retrace just occured - so sleeping 16+8ms should kick you into a more expressive \
condition)
I'm not yet sure where to put that (apparently not init and if we wanted to cache \
it, we'd have to check whether the X server is new - until some driver permits \
changing that at runtime)
Another option was to start with the assumption of triple buffering and measure swaps \
online - if then there's a "significant" amount of swaps that take \
"significantly" more than no time, we can pretty much assume that this is a \
blocking swap and change the state at runtime.</pre> <br />
<p>- Thomas</p>
<br />
<p>On March 28th, 2013, 10:32 p.m. UTC, Thomas Lübking wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="8" \
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url('http://git.reviewboard.kde.org/static/rb/images/review_request_box_top_bg.ab6f3b1072c9.png'); \
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<td>
<div>Review request for kwin, Martin Gräßlin and Ralf Jung.</div>
<div>By Thomas Lübking.</div>
<p style="color: grey;"><i>Updated March 28, 2013, 10:32 p.m.</i></p>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">... for that is not the same (though atm. syncsToVBlank is only used to \
determine the fps interval - other usage pot. for supportInfo etc.)
Also "hasWaitSync" is an implementation detail of GLX - EGL doesn't \
have it.</pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">Compiles and runs. Is part of https://git.reviewboard.kde.org/r/109086/ \
and has been used for pretty long here now.</pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>kwin/composite.cpp <span style="color: grey">(ee885dc)</span></li>
<li>kwin/eglonxbackend.cpp <span style="color: grey">(ecb6e0a)</span></li>
<li>kwin/glxbackend.h <span style="color: grey">(49b897e)</span></li>
<li>kwin/glxbackend.cpp <span style="color: grey">(c68bcee)</span></li>
<li>kwin/scene.h <span style="color: grey">(5d49c40)</span></li>
<li>kwin/scene.cpp <span style="color: grey">(939f000)</span></li>
<li>kwin/scene_opengl.h <span style="color: grey">(409ec3d)</span></li>
<li>kwin/scene_opengl.cpp <span style="color: grey">(3343164)</span></li>
</ul>
<p><a href="http://git.reviewboard.kde.org/r/109783/diff/" style="margin-left: \
3em;">View Diff</a></p>
</td>
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