Touchscreen sample rate and jitter findings

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Scrappy1

Senior Member
Dec 4, 2010
187
29
Here's what I've found related to slow scrolling jitter and the touchscreen. When you first open an app, the very first couple slow scrolling swipes produce very smooth screen animation. It will then get jittery but if you exit the app, then reopen, the smoothness will return. Do this experiment in Contacts app to see what I mean.

Now I found this app called "Touch MultiTest" which reads out the touchscreen sample rate as you move your finger on the screen. When you first open it and do a swipe, you see smooth tracking and a solid sample rate reported greater than 120 Hz. However after a couple swipes the dot response becomes jittery and sample rate drops to something around 100 Hz. Closing and reopening the app gets you back to 120 Hz.

So I think this proves the hardware and software touch loop can produce smooth motion, and it's really sampling at 120 Hz. The big question is what exactly degrades after a couple swipes. In the best case it's some driver or software buffer / interrupt handling that degrades. In the worst case it's related to low level hardware issues. I'm hopeful it's software related. By the way somehow Chrome browser always scrolls smoothly with slow swipes. What is Chrome doing differently than all other apps? Just filtering?
 

Charkatak

Senior Member
Aug 11, 2012
1,562
272
WA
Here's what I've found related to slow scrolling jitter and the touchscreen. When you first open an app, the very first couple slow scrolling swipes produce very smooth screen animation. It will then get jittery but if you exit the app, then reopen, the smoothness will return. Do this experiment in Contacts app to see what I mean.

Now I found this app called "Touch MultiTest" which reads out the touchscreen sample rate as you move your finger on the screen. When you first open it and do a swipe, you see smooth tracking and a solid sample rate reported greater than 120 Hz. However after a couple swipes the dot response becomes jittery and sample rate drops to something around 100 Hz. Closing and reopening the app gets you back to 120 Hz.

So I think this proves the hardware and software touch loop can produce smooth motion, and it's really sampling at 120 Hz. The big question is what exactly degrades after a couple swipes. In the best case it's some driver or software buffer / interrupt handling that degrades. In the worst case it's related to low level hardware issues. I'm hopeful it's software related. By the way somehow Chrome browser always scrolls smoothly with slow swipes. What is Chrome doing differently than all other apps? Just filtering?

Have you tried contacting Essential or possibly using their beta feedback form to tell them about your theory/findings?
 

ChronoReverse

Senior Member
Jun 14, 2010
1,360
247
Our screens sample at 60Hz. We already know this from the AMA's on Reddit. The test app you're using is inaccurate if it reads 120Hz or even 100Hz.

60Hz sampling in of itself shouldn't be a problem either since iPhones (except for the newest ones) sample at 60Hz and everyone knows how smooth they are.

Hopefully there's not some other hardware flaw and it's just Essential's software.
 

Scrappy1

Senior Member
Dec 4, 2010
187
29
Our screens sample at 60Hz. We already know this from the AMA's on Reddit. The test app you're using is inaccurate if it reads 120Hz or even 100Hz.

60Hz sampling in of itself shouldn't be a problem either since iPhones (except for the newest ones) sample at 60Hz and everyone knows how smooth they are.

Hopefully there's not some other hardware flaw and it's just Essential's software.

I don't put much stock in the AMA response since its so vague and nonspecific and could be referring to screen refresh rate (60 Hz) either intentionally or accidentally.

If new iPads and iPhones sample at 120 Hz, it's entirely possible essential panel is sampling at 120 Hz.
 

ChronoReverse

Senior Member
Jun 14, 2010
1,360
247
Try using Touchscreen Benchmark to test and you'll be able to verify the actual samples per second. As a point of comparison, the Galaxy S4 samples at 90Hz and the Shield tablet does a whopping 180Hz!

In any case, it's easy to see that it's not refreshing at 100Hz or 120Hz simply by looking at the number of touch samples that actually appear on the screen. Try it on a faster phone and you can see the higher density of touch responses.

Furthermore, you can't reliably discern the sample rate in the first second so trusting the app saying it's 120Hz and dips to 100Hz is even less reliable than the AMA.
 

Scrappy1

Senior Member
Dec 4, 2010
187
29
Try using Touchscreen Benchmark to test and you'll be able to verify the actual samples per second. As a point of comparison, the Galaxy S4 samples at 90Hz and the Shield tablet does a whopping 180Hz!

In any case, it's easy to see that it's not refreshing at 100Hz or 120Hz simply by looking at the number of touch samples that actually appear on the screen. Try it on a faster phone and you can see the higher density of touch responses.

Furthermore, you can't reliably discern the sample rate in the first second so trusting the app saying it's 120Hz and dips to 100Hz is even less reliable than the AMA.

I invite anyone to do my test and decide for themselves or measure and produce new data. That's what I'm going for here. Not regurgitation of bland statements.
 
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ChronoReverse

Senior Member
Jun 14, 2010
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I invite anyone to do my test and decide for themselves or measure and produce new data. That's what I'm going for here. Not regurgitation of bland statements.
I just invited you to use a different test instead of relying on one that doesn't spit out reasonable numbers.

Does it make more sense that the Essential potentially is using a 120Hz touchscreen which Essential won't confirm despite it being a feather in their caps (since even iPhones only got 120Hz recently) or does it make more sense that Essential is using a slower than average (for Android) panel which their software isn't filtering out as well as Apple's software does? Which is more likely to cause jitter and touch latency?
 
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rignfool

Senior Member
Dec 8, 2010
5,010
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The Poconos
I just invited you to use a different test instead of relying on one that doesn't spit out reasonable numbers.

Does it make more sense that the Essential potentially is using a 120Hz touchscreen which Essential won't confirm despite it being a feather in their caps (since even iPhones only got 120Hz recently) or does it make more sense that Essential is using a slower than average (for Android) panel which their software isn't filtering out as well as Apple's software does? Which is more likely to cause jitter and touch latency?

It's actually that your misunderstanding terminology...

Your mistaking sample rate and refresh rate...

Refresh rate is how many times per second? the screen is redrawn...

Sample rate is how many times per second? the screen reads touches...
 

LNJ

Senior Member
Oct 7, 2007
3,173
808
No way you can tell the difference between 120hz vs 100hz.


Sent from my PH-1 using Tapatalk
 

ChronoReverse

Senior Member
Jun 14, 2010
1,360
247
It's actually that your misunderstanding terminology...

Your mistaking sample rate and refresh rate...

Refresh rate is how many times per second? the screen is redrawn...

Sample rate is how many times per second? the screen reads touches...
No, I'm referring to the touchscreen. Obviously the Essential LCD only refreshes at 60Hz (only the Razer and iPad Pro refreshes at 120Hz) but the touchscreen also samples at 60Hz which is common for lower end Androids (90Hz and 120Hz are the other common sampling rates found in Android devices).

The new iPhone X's OLED still refreshes at 60Hz but has a 120Hz sampling touchscreen which is higher than the 60Hz it used to be in other iOS devices (except for the iPad Pro). I also mentioned the Shield tablet sampling at 180Hz and there's no mobile device with a screen refresh that fast either.
 
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Scrappy1

Senior Member
Dec 4, 2010
187
29
No way you can tell the difference between 120hz vs 100hz.

The drop to 100 Hz after a couple of seconds is "indicative of the problem", not that a 100 Hz rate would not be smooth in a properly designed device. Something comes unhinged at the point we see the drop to 100 Hz. Could be touch buffer / event que is not being serviced fast enough due to low level driver or hardware. Also could be some piece of software in critical path starts consuming more time than allowed, leading to non uniform response. Could be actual stuttering of hardware.

When you exit and then restart an app, the touch event pipleline is flushed, so things are fixed again for a couple of seconds.
 

mhajii210

Senior Member
Sep 19, 2011
494
122
YouTube app

Here's what I've found related to slow scrolling jitter and the touchscreen. When you first open an app, the very first couple slow scrolling swipes produce very smooth screen animation. It will then get jittery but if you exit the app, then reopen, the smoothness will return. Do this experiment in Contacts app to see what I mean.

Now I found this app called "Touch MultiTest" which reads out the touchscreen sample rate as you move your finger on the screen. When you first open it and do a swipe, you see smooth tracking and a solid sample rate reported greater than 120 Hz. However after a couple swipes the dot response becomes jittery and sample rate drops to something around 100 Hz. Closing and reopening the app gets you back to 120 Hz.

So I think this proves the hardware and software touch loop can produce smooth motion, and it's really sampling at 120 Hz. The big question is what exactly degrades after a couple swipes. In the best case it's some driver or software buffer / interrupt handling that degrades. In the worst case it's related to low level hardware issues. I'm hopeful it's software related. By the way somehow Chrome browser always scrolls smoothly with slow swipes. What is Chrome doing differently than all other apps? Just filtering?
I have noticed that if you launch the camera and then open the YouTube app or whatever you're using where you can see the touch scrolling jitters, the touch scrolling is nice and smooth. Then after some time it comes back. The touch scrolling in Chrome is perfect and I wish it was the same everywhere. For some reason the YouTube app performs the worst for me. Chrome must have received an update a while back since I used to get bad touch scrolling on that too. The thing that worries me is some claim touch scrolling is perfectly smooth on their device. Hopefully that's a case of them not noticing it and not a case of actual hardware differences.
 
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Scrappy1

Senior Member
Dec 4, 2010
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I have noticed that if you launch the camera and then open the YouTube app or whatever you're using where you can see the touch scrolling jitters, the touch scrolling is nice and smooth. Then after some time it comes back. The touch scrolling in Chrome is perfect and I wish it was the same everywhere. For some reason the YouTube app performs the worst for me. Chrome must have received an update a while back since I used to get bad touch scrolling on that too. The thing that worries me is some claim touch scrolling is perfectly smooth on their device. Hopefully that's a case of them not noticing it and not a case of actual hardware differences.

Cool tip! I hadn't noticed that. Opening camera then switching to contacts had me scrolling smooth for many minutes. However after a few rounds of tests it lost the magic. I could no longer use camera open first to produce the smooth scrolling. So there are several factors at play here and this could use more investigation. Most of all though this gives me hope the issue can be totally fixed in software.
 

Scrappy1

Senior Member
Dec 4, 2010
187
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I'm starting to think the thing that goes bad and causes choppiness is the rendering pipeline. I enabled "Profile GPU Rendering" and then did a screen capture after scrolling my battery stats in settings for both 1) good condition just after launching settings when scrolling is smooth and 2) bad condition that kicks in after a few seconds when things get choppy. The bad condition shows vastly inflated rendering time which blows the 60 FPS (green line) budget. The largest increase is in red (command issue), but EVERYTHING is inflated in the bad condition. What could cause this?

The captures of the good and bad conditions are attached.
 

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Scrappy1

Senior Member
Dec 4, 2010
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Turns out the reason the rendering pipeline starts taking so long is due to the application thread moving from high performance CPU cluster to the low performance CPU cluster. Using the paid version of System Monitor I opened a floating window of CPU load and freq. I then again opened battery settings and scrolled around in the good and bad state. I can see the CPU load is on the high performance cluster right away (5-8) and those guys are running at 2.4 GHz. Hence everything is smooth. When the jitters set in, the load has moved to low performance cluster (1-4) and they are running much lower clock rate < 1 GHz. I do believe this is probably fairly normal android behavior, but it's obviously tied to the slow scrolling jitters for us. It could be a subtle governor or big.LITTLE thread scheduling issue somehow playing into touch screen weirdness I suppose.

The two captures attached show the issue. One was captured right after launching battery settings when things are smooth and CPUs 5-8 are screaming. Other was captured after things went jittery, and here you can see CPU load that was on 5-8 has moved to 1-4, and clock frequency is much lower. (Hovers between 300 - 1000 Mhz)
 

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rignfool

Senior Member
Dec 8, 2010
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Turns out the reason the rendering pipeline starts taking so long is due to the application thread moving from high performance CPU cluster to the low performance CPU cluster. Using the paid version of System Monitor I opened a floating window of CPU load and freq. I then again opened battery settings and scrolled around in the good and bad state. I can see the CPU load is on the high performance cluster right away (5-8) and those guys are running at 2.4 GHz. Hence everything is smooth. When the jitters set in, the load has moved to low performance cluster (1-4) and they are running much lower clock rate < 1 GHz. I do believe this is probably fairly normal android behavior, but it's obviously tied to the slow scrolling jitters for us. It could be a subtle governor or big.LITTLE thread scheduling issue somehow playing into touch screen weirdness I suppose.

The two captures attached show the issue. One was captured right after launching battery settings when things are smooth and CPUs 5-8 are screaming. Other was captured after things went jittery, and here you can see CPU load that was on 5-8 has moved to 1-4, and clock frequency is much lower. (Hovers between 300 - 1000 Mhz)

Let's try this
@DespairFactor
 

mhajii210

Senior Member
Sep 19, 2011
494
122
GPU governor


Well I can tell you it's not all because of the CPU performance since setting GPU governor to performance on Oreo beta 2 completely gets rid of the touch screen jitters for me. I'm running Oreo beta 2, Rey.R3 Kernel and Magisk 15.2. Using EX Kernel Manager to set GPU governor to performance, I have eliminated the touch scrolling microstutters. Try it out for yourself and see! I also set CPU governor to conservative to compensate for the slightly increased battery usage. Phone is blazing now. https://forum.xda-developers.com/essential-phone/development/kernel-rey-kernel-t3723601 is the link to the kernel.
 
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Scrappy1

Senior Member
Dec 4, 2010
187
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Well I can tell you it's not all because of the CPU performance since setting GPU governor to performance on Oreo beta 2 completely gets rid of the touch screen jitters for me. I'm running Oreo beta 2, Rey.R3 Kernel and Magisk 15.2. Using EX Kernel Manager to set GPU governor to performance, I have eliminated the touch scrolling microstutters. Try it out for yourself and see! I also set CPU governor to conservative to compensate for the slightly increased battery usage. Phone is blazing now. https://forum.xda-developers.com/essential-phone/development/kernel-rey-kernel-t3723601 is the link to the kernel.

Thanks for your input! I would go down the root and tweaks path if I didn't have to use my phone for work with the Google device policy and all. Hoping for some jitter improvement in next official stock update.
 

Hung0702

Senior Member
Mar 1, 2009
568
196
Google Pixel 6
Well I can tell you it's not all because of the CPU performance since setting GPU governor to performance on Oreo beta 2 completely gets rid of the touch screen jitters for me. I'm running Oreo beta 2, Rey.R3 Kernel and Magisk 15.2. Using EX Kernel Manager to set GPU governor to performance, I have eliminated the touch scrolling microstutters. Try it out for yourself and see! I also set CPU governor to conservative to compensate for the slightly increased battery usage. Phone is blazing now. https://forum.xda-developers.com/essential-phone/development/kernel-rey-kernel-t3723601 is the link to the kernel.

Post a video. In all likelihood, it's just placebo effect. I've heard time and time again people claiming that that the slow-scrolling stutter is gone. It's never once been proven. Here's a side-by-side comparison vs the Pixel XL.
 
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    Here's what I've found related to slow scrolling jitter and the touchscreen. When you first open an app, the very first couple slow scrolling swipes produce very smooth screen animation. It will then get jittery but if you exit the app, then reopen, the smoothness will return. Do this experiment in Contacts app to see what I mean.

    Now I found this app called "Touch MultiTest" which reads out the touchscreen sample rate as you move your finger on the screen. When you first open it and do a swipe, you see smooth tracking and a solid sample rate reported greater than 120 Hz. However after a couple swipes the dot response becomes jittery and sample rate drops to something around 100 Hz. Closing and reopening the app gets you back to 120 Hz.

    So I think this proves the hardware and software touch loop can produce smooth motion, and it's really sampling at 120 Hz. The big question is what exactly degrades after a couple swipes. In the best case it's some driver or software buffer / interrupt handling that degrades. In the worst case it's related to low level hardware issues. I'm hopeful it's software related. By the way somehow Chrome browser always scrolls smoothly with slow swipes. What is Chrome doing differently than all other apps? Just filtering?
    4
    Turns out the reason the rendering pipeline starts taking so long is due to the application thread moving from high performance CPU cluster to the low performance CPU cluster. Using the paid version of System Monitor I opened a floating window of CPU load and freq. I then again opened battery settings and scrolled around in the good and bad state. I can see the CPU load is on the high performance cluster right away (5-8) and those guys are running at 2.4 GHz. Hence everything is smooth. When the jitters set in, the load has moved to low performance cluster (1-4) and they are running much lower clock rate < 1 GHz. I do believe this is probably fairly normal android behavior, but it's obviously tied to the slow scrolling jitters for us. It could be a subtle governor or big.LITTLE thread scheduling issue somehow playing into touch screen weirdness I suppose.

    The two captures attached show the issue. One was captured right after launching battery settings when things are smooth and CPUs 5-8 are screaming. Other was captured after things went jittery, and here you can see CPU load that was on 5-8 has moved to 1-4, and clock frequency is much lower. (Hovers between 300 - 1000 Mhz)
    2

    I think we can move the touchscreen to it's own workqueue, but not sure if it'll handle this.
    1
    Try using Touchscreen Benchmark to test and you'll be able to verify the actual samples per second. As a point of comparison, the Galaxy S4 samples at 90Hz and the Shield tablet does a whopping 180Hz!

    In any case, it's easy to see that it's not refreshing at 100Hz or 120Hz simply by looking at the number of touch samples that actually appear on the screen. Try it on a faster phone and you can see the higher density of touch responses.

    Furthermore, you can't reliably discern the sample rate in the first second so trusting the app saying it's 120Hz and dips to 100Hz is even less reliable than the AMA.

    I invite anyone to do my test and decide for themselves or measure and produce new data. That's what I'm going for here. Not regurgitation of bland statements.
    1
    YouTube app

    Here's what I've found related to slow scrolling jitter and the touchscreen. When you first open an app, the very first couple slow scrolling swipes produce very smooth screen animation. It will then get jittery but if you exit the app, then reopen, the smoothness will return. Do this experiment in Contacts app to see what I mean.

    Now I found this app called "Touch MultiTest" which reads out the touchscreen sample rate as you move your finger on the screen. When you first open it and do a swipe, you see smooth tracking and a solid sample rate reported greater than 120 Hz. However after a couple swipes the dot response becomes jittery and sample rate drops to something around 100 Hz. Closing and reopening the app gets you back to 120 Hz.

    So I think this proves the hardware and software touch loop can produce smooth motion, and it's really sampling at 120 Hz. The big question is what exactly degrades after a couple swipes. In the best case it's some driver or software buffer / interrupt handling that degrades. In the worst case it's related to low level hardware issues. I'm hopeful it's software related. By the way somehow Chrome browser always scrolls smoothly with slow swipes. What is Chrome doing differently than all other apps? Just filtering?
    I have noticed that if you launch the camera and then open the YouTube app or whatever you're using where you can see the touch scrolling jitters, the touch scrolling is nice and smooth. Then after some time it comes back. The touch scrolling in Chrome is perfect and I wish it was the same everywhere. For some reason the YouTube app performs the worst for me. Chrome must have received an update a while back since I used to get bad touch scrolling on that too. The thing that worries me is some claim touch scrolling is perfectly smooth on their device. Hopefully that's a case of them not noticing it and not a case of actual hardware differences.