Public bug reported:
Using a vanilla installation of Ubuntu 20.04, the timestamps of input
events from my Apple "Magic Trackpad" - 1st generation, connected over
Bluetooth - are jittery.
This is a regression, the timestamps were fine when using Ubuntu 19.10.
I bisected the bug.
- The problem starts with upstream kernel commit 3b51c44bd693 ("Input: allow
drivers specify timestamp for input events"). After that commit, the same
timestamp is always emitted.
- This was partially fixed in commit 4370b231d100 ("Input: reset device
timestamp on sync"), however ever since then the timestamps are jittery.
The problem still exists in the current upstream 'master' (commit
c45e8bccecaf).
The following patch fixes the bug, however this is obviously a hack. It
effectively reverts commit 3b51c44bd693:
diff --git a/drivers/input/input.c b/drivers/input/input.c
index 3cfd2c18eebd..8890195547d6 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -1958,7 +1958,7 @@ ktime_t *input_get_timestamp(struct input_dev *dev)
{
const ktime_t invalid_timestamp = ktime_set(0, 0);
- if (!ktime_compare(dev->timestamp[INPUT_CLK_MONO], invalid_timestamp))
+ // if (!ktime_compare(dev->timestamp[INPUT_CLK_MONO],
invalid_timestamp))
input_set_timestamp(dev, ktime_get());
return dev->timestamp;
Steps to reproduce
------------------
I used the following script as a reproducer. It relies on libinput-
debug-events. This script measures the time delta between consecutive
input events, then prints a "histogram" of these deltas.
#!/bin/bash
# log file name
logFile=${1:-~/Downloads/`uname -r`}
echo logFile=$logFile
if [[ "$1" == '' ]]; then
echo record
# log some events
sudo libinput debug-events | grep POINTER | tee $logFile
fi
# process the results
lastN=0
for f in `cat $logFile | awk '{print $3}' | sed "s/s//g" | sed "s/+//g"`;
do
echo "$f-$lastN" | bc;
lastN=$f;
done | sort | uniq -c
1. Pair an external Apple Trackpad over Blutooth.
2. Run the above script
3. Move your finger in circles on the touchpad for a few seconds
4. Press ctrl+c
An example output of this script before the regression
------------------------------------------------------
2 .010
371 .011
127 .012
1 .876
The above output means that: 2 times the delta was 10ms, 371 times 11ms,
127 times 12ms and 1 time 876ms. This corresponds well with the
Trackpad's ~90Hz polling rate.
An example output of this script after the regression
-----------------------------------------------------
3 .003
12 .004
16 .005
14 .006
21 .007
16 .008
20 .009
13 .010
359 .011
47 .012
20 .013
17 .014
21 .015
14 .016
16 .017
15 .018
2 .019
1 .020
38 .022
21 .023
1 1.060
I suspect that other input devices might be affected as well.
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-28-generic 5.4.0-28.32
ProcVersionSignature: Ubuntu 5.4.0-28.32-generic 5.4.30
Uname: Linux 5.4.0-28-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: yariv 1783 F.... pulseaudio
CasperMD5CheckResult: skip
Date: Sat May 2 13:58:34 2020
InstallationDate: Installed on 2019-07-13 (293 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
MachineType: Gigabyte Technology Co., Ltd. Z170X-UD5 TH
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-28-generic
root=UUID=6deee348-bb50-4b88-837b-108413e4d8f2 ro quiet splash
btusb.enable_autosuspend=0 vt.handoff=7
RelatedPackageVersions:
linux-restricted-modules-5.4.0-28-generic N/A
linux-backports-modules-5.4.0-28-generic N/A
linux-firmware 1.187
RfKill:
0: hci0: Bluetooth
Soft blocked: no
Hard blocked: no
SourcePackage: linux
UpgradeStatus: Upgraded to focal on 2020-04-28 (3 days ago)
dmi.bios.date: 03/09/2018
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: F22g
dmi.board.asset.tag: Default string
dmi.board.name: Z170X-UD5 TH-CF
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.asset.tag: Default string
dmi.chassis.type: 3
dmi.chassis.vendor: Default string
dmi.chassis.version: Default string
dmi.modalias:
dmi:bvnAmericanMegatrendsInc.:bvrF22g:bd03/09/2018:svnGigabyteTechnologyCo.,Ltd.:pnZ170X-UD5TH:pvrDefaultstring:rvnGigabyteTechnologyCo.,Ltd.:rnZ170X-UD5TH-CF:rvrx.x:cvnDefaultstring:ct3:cvrDefaultstring:
dmi.product.family: Default string
dmi.product.name: Z170X-UD5 TH
dmi.product.sku: Default string
dmi.product.version: Default string
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug focal wayland-session
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https://bugs.launchpad.net/bugs/1876449
Title:
Apple external Trackpad event timestamps are jittery
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