Would it be possible to utilize freesync/gsync/vrr to further optimize compton?

[Kommynct]

This is mostly a technical curiosity, honestly, i'd be interested if you could actually eliminate input latency from vsync, could that be done?

[aufkrawall]

One reason for compositors being blacklisted for VRR in the driver is because they have insane variations between the presentation duration of different frames, as they throttle compositing when the screen content doesn't change every frame.
That can cause flickering with VRR, since there is a difference in brightness between lower and higher refresh rates.

Though it might work with some displays, and I agree that it would be cool to get rid of vsync lag entirely. It might already work by simply removing Compton from the driver's blacklist and setting a refreshrate below the display's maximum in Compton's config.

[yshui]

Looks to me your can just enable vrr in mesa's config file (if you are using AMD, not sure about the other drivers), I don't think there is anything compton needs to do in particular?

[grmat]

As the Linux FreeSync implementation currently doesn't offer implicit low framerate compensation (IIRC), so maybe it would help if the compositor queried the monitor's minimum refresh rate (and/or make it configurable) and make sure to refresh at this minimum rate. That'd also be a waste of energy though. Currently compton doesn't refresh at all if there is no change and I haven't checked the outcome. I'm also not sure if this feature is that desired on desktop usage to justify including this functionality into compton.

Another issue is that a hardware cursor won't make the compositor update (unless the cursor changes state of any hovered object) and if the mouse cursor is stuttering at the monitor's minimum refresh rate as the compositor is effectively handling it, this will surely impact the user experience.

[aufkrawall]

It seems manually setting the refresh rate doesn't force Compton to actually render at that rate (anymore?).
It might work with libstrangle, which offers an fps limiter:
https://gitlab.com/torkel104/libstrangle

[yshui]

What will happen right now, if you just remove compton from the blacklist?

[grmat]

I haven't done extensive testing, just gave it a quick shot. It will refresh at minimum rate, which is 35 Hz for my monitor and very unpleasant to use with a hardware cursor. It didn't eliminate the lag iirc. I'll see if I can do better testing but it'll take a while until I have access to the hardware again

[yshui]

There is also this option --benchmark, which takes a frame count as argument, that forces compton to render at the maximum rate for a given number of frame then exit.

Maybe give that a try.

[sandsmark]

you can use Application Profiles in nvidia-settings to disable gsync only for picom (also turn on the gsync indicator to verify that it doesn't use gsync).

[yshui]

Can someone with a VRR monitor paste their xrandr --verbose output?

[Kommynct]

Screen 0: minimum 16 x 16, current 4480 x 1440, maximum 32767 x 32767
XWAYLAND0 connected 2560x1440+0+0 (0x24) normal (normal left inverted right x axis y axis) 600mm x 340mm
Identifier: 0x21
Timestamp: 7832
Subpixel: unknown
Gamma: 1.0:1.0:1.0
Brightness: 0.0
Clones:
CRTC: 0
CRTCs: 0
Transform: 1.000000 0.000000 0.000000
0.000000 1.000000 0.000000
0.000000 0.000000 1.000000
filter:
non-desktop: 0
supported: 0, 1
2560x1440 (0x24) 807.750MHz -HSync +VSync *current +preferred
h: width 2560 start 2792 end 3072 total 3584 skew 0 clock 225.38KHz
v: height 1440 start 1443 end 1448 total 1567 clock 143.83Hz

i'm on wayland i hope this is still useful

[yshui]

@Kommynct thanks, but I need someone who runs X natively.

[Kommynct]

If nobody else bothers I can do this tomorrow

[accelbread]

Here is mine, native X with 3 VRR monitors.

`xrandr --verbose`

Screen 0: minimum 320 x 200, current 11520 x 2160, maximum 16384 x 16384
DisplayPort-2 connected primary 3840x2160+0+0 (0x59) normal (normal left inverted right x axis y axis) 600mm x 340mm
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        TearFree: on
                supported: off, on, auto
        vrr_capable: 1
                range: (0, 1)
        max bpc: 8
                range: (8, 16)
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        underscan hborder: 0
                range: (0, 128)
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                supported: off, on, auto
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                supported: None, Full, Center, Full aspect
        link-status: Good
                supported: Good, Bad
        CONNECTOR_ID: 80
                supported: 80
        non-desktop: 0
                range: (0, 1)
  3840x2160 (0x59) 533.250MHz +HSync -VSync *current +preferred
        h: width  3840 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  60.00Hz
  3840x2160 (0x5a) 266.640MHz +HSync -VSync
        h: width  3840 start 3848 end 3992 total 4000 skew    0 clock  66.66KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  30.00Hz
  2560x1440 (0x5b) 241.500MHz +HSync -VSync
        h: width  2560 start 2608 end 2640 total 2720 skew    0 clock  88.79KHz
        v: height 1440 start 1443 end 1448 total 1481           clock  59.95Hz
  1920x1200 (0x5c) 533.250MHz +HSync -VSync
        h: width  1920 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
  1920x1080 (0x5d) 148.500MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
  1920x1080 (0x5e) 148.352MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.43KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  59.94Hz
  1600x1200 (0x5f) 533.250MHz +HSync -VSync
        h: width  1600 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
  1680x1050 (0x60) 533.250MHz +HSync -VSync
        h: width  1680 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1050 start 2214 end 2219 total 2222           clock  60.00Hz
  1600x900 (0x61) 108.000MHz +HSync +VSync
        h: width  1600 start 1624 end 1704 total 1800 skew    0 clock  60.00KHz
        v: height  900 start  901 end  904 total 1000           clock  60.00Hz
  1280x1024 (0x62) 108.000MHz +HSync +VSync
        h: width  1280 start 1328 end 1440 total 1688 skew    0 clock  63.98KHz
        v: height 1024 start 1025 end 1028 total 1066           clock  60.02Hz
  1440x900 (0x63) 533.250MHz +HSync -VSync
        h: width  1440 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height  900 start 2214 end 2219 total 2222           clock  60.00Hz
  1280x800 (0x64) 83.500MHz -HSync +VSync
        h: width  1280 start 1352 end 1480 total 1680 skew    0 clock  49.70KHz
        v: height  800 start  803 end  809 total  831           clock  59.81Hz
  1152x864 (0x65) 81.768MHz -HSync +VSync
        h: width  1152 start 1216 end 1336 total 1520 skew    0 clock  53.79KHz
        v: height  864 start  867 end  871 total  897           clock  59.97Hz
  1280x720 (0x66) 74.250MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  45.00KHz
        v: height  720 start  725 end  730 total  750           clock  60.00Hz
  1280x720 (0x67) 74.176MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  44.96KHz
        v: height  720 start  725 end  730 total  750           clock  59.94Hz
  1024x768 (0x68) 65.000MHz -HSync -VSync
        h: width  1024 start 1048 end 1184 total 1344 skew    0 clock  48.36KHz
        v: height  768 start  771 end  777 total  806           clock  60.00Hz
  800x600 (0x69) 40.000MHz +HSync +VSync
        h: width   800 start  840 end  968 total 1056 skew    0 clock  37.88KHz
        v: height  600 start  601 end  605 total  628           clock  60.32Hz
  720x480 (0x6a) 27.027MHz -HSync -VSync
        h: width   720 start  736 end  798 total  858 skew    0 clock  31.50KHz
        v: height  480 start  489 end  495 total  525           clock  60.00Hz
  720x480 (0x6b) 27.000MHz -HSync -VSync
        h: width   720 start  736 end  798 total  858 skew    0 clock  31.47KHz
        v: height  480 start  489 end  495 total  525           clock  59.94Hz
  640x480 (0x6c) 25.200MHz -HSync -VSync
        h: width   640 start  656 end  752 total  800 skew    0 clock  31.50KHz
        v: height  480 start  490 end  492 total  525           clock  60.00Hz
  640x480 (0x6d) 25.175MHz -HSync -VSync
        h: width   640 start  656 end  752 total  800 skew    0 clock  31.47KHz
        v: height  480 start  490 end  492 total  525           clock  59.94Hz
DisplayPort-3 connected 3840x2160+3840+0 (0x59) normal (normal left inverted right x axis y axis) 600mm x 340mm
        Identifier: 0x55
        Timestamp:  11908
        Subpixel:   unknown
        Gamma:      1.0:1.1:1.3
        Brightness: 1.0
        Clones:
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        CTM: 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0
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        TearFree: on
                supported: off, on, auto
        vrr_capable: 1
                range: (0, 1)
        max bpc: 8
                range: (8, 16)
        underscan vborder: 0
                range: (0, 128)
        underscan hborder: 0
                range: (0, 128)
        underscan: off
                supported: off, on, auto
        scaling mode: None
                supported: None, Full, Center, Full aspect
        link-status: Good
                supported: Good, Bad
        CONNECTOR_ID: 85
                supported: 85
        non-desktop: 0
                range: (0, 1)
  3840x2160 (0x59) 533.250MHz +HSync -VSync *current +preferred
        h: width  3840 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  60.00Hz
  3840x2160 (0x5a) 266.640MHz +HSync -VSync
        h: width  3840 start 3848 end 3992 total 4000 skew    0 clock  66.66KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  30.00Hz
  2560x1440 (0x5b) 241.500MHz +HSync -VSync
        h: width  2560 start 2608 end 2640 total 2720 skew    0 clock  88.79KHz
        v: height 1440 start 1443 end 1448 total 1481           clock  59.95Hz
  1920x1200 (0x5c) 533.250MHz +HSync -VSync
        h: width  1920 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
  1920x1080 (0x5d) 148.500MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
  1920x1080 (0x5e) 148.352MHz +HSync +VSync
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.43KHz
        v: height 1080 start 1084 end 108CLICK ME9 total 1125           clock  59.94Hz
  1600x1200 (0x5f) 533.250MHz +HSync -VSync
        h: width  1600 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
  1680x1050 (0x60) 533.250MHz +HSync -VSync
        h: width  1680 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1050 start 2214 end 2219 total 2222           clock  60.00Hz
  1600x900 (0x61) 108.000MHz +HSync +VSync
        h: width  1600 start 1624 end 1704 total 1800 skew    0 clock  60.00KHz
        v: height  900 start  901 end  904 total 1000           clock  60.00Hz
  1280x1024 (0x62) 108.000MHz +HSync +VSync
        h: width  1280 start 1328 end 1440 total 1688 skew    0 clock  63.98KHz
        v: height 1024 start 1025 end 1028 total 1066           clock  60.02Hz
  1440x900 (0x63) 533.250MHz +HSync -VSync
        h: width  1440 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height  900 start 2214 end 2219 total 2222           clock  60.00Hz
  1280x800 (0x64) 83.500MHz -HSync +VSync
        h: width  1280 start 1352 end 1480 total 1680 skew    0 clock  49.70KHz
        v: height  800 start  803 end  809 total  831           clock  59.81Hz
  1152x864 (0x65) 81.768MHz -HSync +VSync
        h: width  1152 start 1216 end 1336 total 1520 skew    0 clock  53.79KHz
        v: height  864 start  867 end  871 total  897           clock  59.97Hz
  1280x720 (0x66) 74.250MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  45.00KHz
        v: height  720 start  725 end  730 total  750           clock  60.00Hz
  1280x720 (0x67) 74.176MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  44.96KHz
        v: height  720 start  725 end  730 total  750           clock  59.94Hz
  1024x768 (0x68) 65.000MHz -HSync -VSync
        h: width  1024 start 1048 end 1184 total 1344 skew    0 clock  48.36KHz
        v: height  768 start  771 end  777 total  806           clock  60.00Hz
  800x600 (0x69) 40.000MHz +HSync +VSync
        h: width   800 start  840 end  968 total 1056 skew    0 clock  37.88KHz
        v: height  600 start  601 end  605 total  628           clock  60.32Hz
  720x480 (0x6a) 27.027MHz -HSync -VSync
        h: width   720 start  736 end  798 total  858 skew    0 clock  31.50KHz
        v: height  480 start  489 end  495 total  525           clock  60.00Hz
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        v: height  480 start  489 end  495 total  525           clock  59.94Hz
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        v: height  480 start  490 end  492 total  525           clock  60.00Hz
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        h: width   640 start  656 end  752 total  800 skew    0 clock  31.47KHz
        v: height  480 start  490 end  492 total  525           clock  59.94Hz
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        Identifier: 0x56
        Timestamp:  11908
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        h: width  3840 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  60.00Hz
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        h: width  3840 start 3848 end 3992 total 4000 skew    0 clock  66.66KHz
        v: height 2160 start 2214 end 2219 total 2222           clock  30.00Hz
  2560x1440 (0x5b) 241.500MHz +HSync -VSync
        h: width  2560 start 2608 end 2640 total 2720 skew    0 clock  88.79KHz
        v: height 1440 start 1443 end 1448 total 1481           clock  59.95Hz
  1920x1200 (0x5c) 533.250MHz +HSync -VSync
        h: width  1920 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
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        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
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        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.43KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  59.94Hz
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        h: width  1600 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 1200 start 2214 end 2219 total 2222           clock  60.00Hz
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        v: height 1050 start 2214 end 2219 total 2222           clock  60.00Hz
  1600x900 (0x61) 108.000MHz +HSync +VSync
        h: width  1600 start 1624 end 1704 total 1800 skew    0 clock  60.00KHz
        v: height  900 start  901 end  904 total 1000           clock  60.00Hz
  1280x1024 (0x62) 108.000MHz +HSync +VSync
        h: width  1280 start 1328 end 1440 total 1688 skew    0 clock  63.98KHz
        v: height 1024 start 1025 end 1028 total 1066           clock  60.02Hz
  1440x900 (0x63) 533.250MHz +HSync -VSync
        h: width  1440 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height  900 start 2214 end 2219 total 2222           clock  60.00Hz
  1280x800 (0x64) 83.500MHz -HSync +VSync
        h: width  1280 start 1352 end 1480 total 1680 skew    0 clock  49.70KHz
        v: height  800 start  803 end  809 total  831           clock  59.81Hz
  1152x864 (0x65) 81.768MHz -HSync +VSync
        h: width  1152 start 1216 end 1336 total 1520 skew    0 clock  53.79KHz
        v: height  864 start  867 end  871 total  897           clock  59.97Hz
  1280x720 (0x66) 74.250MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  45.00KHz
        v: height  720 start  725 end  730 total  750           clock  60.00Hz
  1280x720 (0x67) 74.176MHz +HSync +VSync
        h: width  1280 start 1390 end 1430 total 1650 skew    0 clock  44.96KHz
        v: height  720 start  725 end  730 total  750           clock  59.94Hz
  1024x768 (0x68) 65.000MHz -HSync -VSync
        h: width  1024 start 1048 end 1184 total 1344 skew    0 clock  48.36KHz
        v: height  768 start  771 end  777 total  806           clock  60.00Hz
  800x600 (0x69) 40.000MHz +HSync +VSync
        h: width   800 start  840 end  968 total 1056 skew    0 clock  37.88KHz
        v: height  600 start  601 end  605 total  628           clock  60.32Hz
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        v: height  480 start  489 end  495 total  525           clock  60.00Hz
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        v: height  480 start  490 end  492 total  525           clock  60.00Hz
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        v: height  480 start  490 end  492 total  525           clock  59.94Hz
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        CONNECTOR_ID: 95
                supported: 95
        non-desktop: 0
                range: (0, 1)

[yshui]

@accelbread Thanks!

[Monsterovich]

So far, there is no way to make picom work with VRR other than using the unredir-if-possible parameter to make VRR work at least in full-screen windows. This disables compositing and the monitor gets the FPS of the current opened window. I don't know how, but somehow compiz doesn't have this problem, VRR works in full screen windows without disabling compositing.

Is there a practice of using VRR in non full-screen window enviroments?

[yshui]

picom can't use VRR because drivers are specifically disabling it for picom. and they have a good reason to do so, because picom doesn't have a fixed update rate (it only updates when something on screen changes), i think that's messing up the refresh rate somehow. i think people are saying the screen updates very slowly.

now we have frame pacing implemented maybe there is something we can do to improve the situation, but i am not sure. i'll left this as a TODO, maybe someone can take on this if they are interested.

[Monsterovich]

cursor doesn't necessarily raise refresh rate. in fact the cursor has nothing to do with picom, it doesn't even go through compositing.

That's the problem, the cursor moves at ~40fps, even though the screen refresh rate should ideally be maxed out when moving.

[Monsterovich]

what happens when you are doing something that constantly updates the screen? like playing a video or a game or something.

Even when I just scroll down the list in the browser the frequency goes up to 110-144hz.

With games, too, everything is fine, but you need an option to set the minimum frequency value, so that the frequency does not change rapidly from 45hz to 144hz, the monitor doesn't like it and it starts to flicker.

You can "fix" it by editing the EDID, but it would be better if the compositor did it.

https://forum.level1techs.com/t/how-to-fix-freesync-lfc-screen-blanking-issues-using-wxedid-linux-ubuntu/177867

[yshui]

That's the problem, the cursor moves at ~40fps

So your suggestion is picom should detect the cursor is moving and render more frequently? I think that's the driver's responsibility, picom isn't even rendering the cursor why should it worry about it?

[Monsterovich]

So your suggestion is picom should detect the cursor is moving and render more frequently?

Yes. https://github.com/dahenry/gl-gsync-demo/blob/master/main.c#L358

That's just how it's done in the demo to test gsync.

I think that's the driver's responsibility, picom isn't even rendering the cursor why should it worry about it?

Their responsibility ended exactly when they blacklisted all known linux compositors and nailed the problem.

https://gitlab.freedesktop.org/drm/amd/-/issues/2186#note_1971490

Apparently VRR is not friendly with hardware cursors and the only way around it is to repaint stuff.

I wonder if there is an API to directly control the refresh rate of a VRR monitor?

[yshui]

hmm, interesting. i think if we need to support vrr is a minimal refresh rate, it probably wouldn't be too much work.

[Stebalien]

As of the AMD cursor fixes in Linux 6.11, cursor movements under picom have been buttery smooth even with VRR enabled. My .drirc:

<?xml version="1.0" standalone="yes"?>

<driconf>
    <device>
        <application name="picom" executable="picom">
            <option name="adaptive_sync" value="true" />
        </application>
    </device>
</driconf>

[Monsterovich]

As of the AMD cursor fixes in Linux 6.11, cursor movements under picom have been buttery smooth even with VRR enabled. My .drirc:

<?xml version="1.0" standalone="yes"?>

<driconf>
    <device>
        <application name="picom" executable="picom">
            <option name="adaptive_sync" value="true" />
        </application>
    </device>
</driconf>

Did they make it so that moving the cursor also changes the refresh rate of the screen?

[Stebalien]

The changes hare here: https://gitlab.freedesktop.org/drm/amd/-/issues/2186#note_2368021

I'm not entirely sure what they did.

[Stebalien]

Hm. Ok, well, it's better but now it's back to being a bit choppy. My screen is configured with a minimum 30fps frame-rate which is why it's usually pretty usable anyways.

Something must have been forcing screen updates (e.g., an animation).