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Tasklist

FS#70728 - Thinkpad T495 Elantech touchpad generates excessive IRQ requests

Attached to Project: Arch Linux
Opened by Ennis Massey (microtx) - Thursday, 06 May 2021, 01:09 GMT
Last edited by Andreas Radke (AndyRTR) - Friday, 07 May 2021, 08:02 GMT
Task Type Bug Report
Category Kernel
Status Assigned
Assigned To Jan Alexander Steffens (heftig)
Architecture x86_64
Severity Medium
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 0%
Votes 0
Private No

Details

Description:
The touchpad on the Thinkpad T495 generates an excessive number of IRQ's when in use. I did some quick measurements and it seems to come in at around 470 interrupts per second when the
trackpad is being used. I've sent an email to Elantech (who makes the touchpad) to see if they can provide help. I've tried to look for a solution, but haven't found much outside of other people running into the same issue.


Additional info:
* Kernel Version: 5.11.16-arch1-1
* Laptop Model: Thinkpad T495


Steps to reproduce:
- Using a T495 laptop, watch `lsirq`
- Move the mouse around using the touchpad
- The IRQ for the i8042 chip should rapidly increase.

Also attached relevant lines from dmesg.
This task depends upon

Comment by Jan Alexander Steffens (heftig) - Friday, 07 May 2021, 14:58 GMT
I'm pretty sure this is normal. My synaptics i2c touchpad generates over 9000 interrupts per second while in use.
Comment by Ennis Massey (microtx) - Saturday, 08 May 2021, 00:34 GMT
The issue here I've found is that excessive interrupts consume up to and over 1 watt of power, at least according to powertop. On a battery powered device this can quite noticeably decrease battery life. I've found other reports on other sites reporting the same problem as well as 100% CPU usage handling the interrupts. Lowering /sys/bus/serio/drivers/psmouse/serio2/rate helps, although below a value of 40 the responsiveness suffers noticeably. The interrupts also continue for some time after I stop touching the touchpad, indicating it's sending messages that do nothing to some extent.

Some other similar reports (although not identical):
- https://bugs.launchpad.net/ubuntu/+source/linux/+bug/194489
- https://askubuntu.com/questions/1247208/touchpad-causes-huge-amount-of-interrupts-and-high-power-usage

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