I recently noticed that one of my CPUs was idling at around 85-90% and according to top the usage was coming from interrupts, so just like in this question I used a combination of dmesg and periodically cating /proc/interrupts and found out this:
CPU0 CPU1 CPU2 CPU3
0: 17 0 0 0 IR-IO-APIC 2-edge timer
1: 11548 0 2429 0 IR-IO-APIC 1-edge i8042
8: 0 0 0 1 IR-IO-APIC 8-edge rtc0
9: 7 16 0 0 IR-IO-APIC 9-fasteoi acpi
12: 14530 108887 0 0 IR-IO-APIC 12-edge i8042
16: 78464100 0 0 11702812 IR-IO-APIC 16-fasteoi idma64.0, i2c_designware.0, i801_smbus
120: 0 0 0 0 DMAR-MSI 0-edge dmar0
121: 0 0 0 0 DMAR-MSI 1-edge dmar1
As you can see, IRQ #16 is sending interrupts like crazy (every time the CPU wakes up from S3 it seems to start spamming a different CPU), I also found out that my touchpad uses the same IRQ and if the I2C mode is enabled (or advanced mode, according to my BIOS), it randomly stops working with the following messages (from dmesg):
[ 167.851139] irq 16: nobody cared (try booting with the "irqpoll" option)
[ 167.851158] CPU: 2 PID: 3874 Comm: firefox Not tainted 4.15.3-300.fc27.x86_64 #1
[ 167.851160] Hardware name: Acer Aspire E5-575/Ironman_SK , BIOS V1.04 04/26/2016
[ 167.851162] Call Trace:
[ 167.851171] <IRQ>
[ 167.851185] dump_stack+0x5c/0x85
[ 167.851193] __report_bad_irq+0x30/0xc0
[ 167.851196] note_interrupt+0x235/0x280
[ 167.851198] handle_irq_event_percpu+0x51/0x70
[ 167.851201] handle_irq_event+0x27/0x50
[ 167.851204] handle_fasteoi_irq+0x6b/0x120
[ 167.851209] handle_irq+0xaf/0x120
[ 167.851214] do_IRQ+0x41/0xc0
[ 167.851219] common_interrupt+0xa2/0xa2
[ 167.851222] </IRQ>
[ 167.851224] RIP: 0010:_raw_spin_lock+0x10/0x20
[ 167.851226] RSP: 0000:ffffa85a857dfdd0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffdb
[ 167.851230] RAX: 0000000000000000 RBX: ffff8d0a268930c8 RCX: 00003ffffffff000
[ 167.851231] RDX: 0000000000000001 RSI: 8000000000000025 RDI: ffffd21648d7ca70
[ 167.851232] RBP: ffffd2164892e100 R08: 0000000000000000 R09: 0000000000171800
[ 167.851233] R10: 0000000000271800 R11: 0000000000001000 R12: 0000000000000000
[ 167.851234] R13: 8000000224b84867 R14: ffffd21648d7ca70 R15: ffff8d0a35f29810
[ 167.851244] __handle_mm_fault+0xa4c/0x1290
[ 167.851249] handle_mm_fault+0xaa/0x1f0
[ 167.851255] __do_page_fault+0x25d/0x4e0
[ 167.851262] ? SyS_mmap_pgoff+0xfb/0x250
[ 167.851264] do_page_fault+0x32/0x110
[ 167.851267] ? page_fault+0x36/0x60
[ 167.851269] page_fault+0x4c/0x60
[ 167.851272] RIP: 0033:0x7ff86dc0b205
[ 167.851273] RSP: 002b:00007ffe6493e888 EFLAGS: 00010206
[ 167.851276] handlers:
[ 167.851291] [<0000000061f0cd43>] idma64_irq [idma64]
[ 167.851296] [<000000006909bb35>] i2c_dw_isr
[ 167.851302] [<00000000ee17d26d>] i801_isr [i2c_i801]
[ 167.851304] Disabling IRQ #16
Is this a hardware issue? What can I do?
Finally I have a chance to dig more into this, by running lspci -nnkv I found out 2 devices that are using IRQ 16:
00:15.0 Signal processing controller [1180]: Intel Corporation Sunrise Point-LP Serial IO I2C Controller #0 [8086:9d60] (rev 21)
Subsystem: Acer Incorporated [ALI] Device [1025:1094]
Flags: fast devsel, IRQ 16
Memory at a132b000 (64-bit, non-prefetchable) [size=4K]
Capabilities: [80] Power Management version 3
Capabilities: [90] Vendor Specific Information: Len=14 <?>
Kernel driver in use: intel-lpss
Kernel modules: intel_lpss_pci
and:
00:1f.4 SMBus [0c05]: Intel Corporation Sunrise Point-LP SMBus [8086:9d23] (rev 21)
Subsystem: Acer Incorporated [ALI] Device [1025:1094]
Flags: medium devsel, IRQ 16
Memory at a132e000 (64-bit, non-prefetchable) [size=256]
I/O ports at 4040 [size=32]
Kernel driver in use: i801_smbus
Kernel modules: i2c_i801
The problem seems to go away if I unload the intel_lpss_pci module i.e. rmmod intel_lpss_pci, but of course the touchpad would stop working. But I guess it's better than having a CPU always at 100%.
modprobe intel_lpss_pci.