Not sure that's completely related, but would assume at least partially.
I have two mini-servers, one with a Supermicro A2SDi-8C-HLN4F (Atom C3758), and the other one with an older Supermicro A1SRM-2758F (Atom C2758F).

I upgraded both from Debian Buster (kernel 4.19.194-3) to Bullseye (5.10.46-5). No issue on the C3758, but i was faced with severe performance regression on the C2758F.

When running 5.10 on the C2758F, /proc/interrupts shows about 100k interrupts per second for 'IO-APIC 18-fasteoi i801_smbus', and overall performance suffers a lot (e.g. iperf between two KVM virtual machines bridged together is 93% slower with 5.10 than with 4.19).

So far i was getting around the issue by blocklisting i2c_i801. After i found this, i tried adding the disable_features=0x10 option, and that worked too.

I'm not using jc42 at all, sensors thresholds are set to correct values by the distro tools.

# i2cdetect -l

# sensors
nvme-pci-0400
Adapter: PCI adapter
Composite:    +30.9°C  (low  = -273.1°C, high = +84.8°C)
                       (crit = +84.8°C)
Sensor 1:     +30.9°C  (low  = -273.1°C, high = +65261.8°C)
Sensor 2:     +31.9°C  (low  = -273.1°C, high = +65261.8°C)

coretemp-isa-0000
Adapter: ISA adapter
Core 0:       +48.0°C  (high = +98.0°C, crit = +98.0°C)
Core 1:       +48.0°C  (high = +98.0°C, crit = +98.0°C)
Core 2:       +48.0°C  (high = +98.0°C, crit = +98.0°C)
Core 3:       +48.0°C  (high = +98.0°C, crit = +98.0°C)
Core 4:       +47.0°C  (high = +98.0°C, crit = +98.0°C)
Core 5:       +46.0°C  (high = +98.0°C, crit = +98.0°C)
Core 6:       +47.0°C  (high = +98.0°C, crit = +98.0°C)
Core 7:       +47.0°C  (high = +98.0°C, crit = +98.0°C)

# dmesg | egrep -i '(smbus|i801)'
[    2.226240] ismt_smbus 0000:00:13.0: enabling device (0000 -> 0002)
[    2.229927] i801_smbus 0000:00:1f.3: enabling device (0000 -> 0003)
[    2.230089] i801_smbus 0000:00:1f.3: SPD Write Disable is set
[    2.230136] i801_smbus 0000:00:1f.3: SMBus using PCI interrupt

~# lspci -nn | grep SMBus
00:13.0 System peripheral [0880]: Intel Corporation Atom processor C2000 SMBus 2.0 [8086:1f15] (rev 03)
00:1f.3 SMBus [0c05]: Intel Corporation Atom processor C2000 PCU SMBus [8086:1f3c] (rev 03)

# lspci -xxx -s 00:13.0
00:13.0 System peripheral: Intel Corporation Atom processor C2000 SMBus 2.0 (rev 03)
00: 86 80 15 1f 06 04 10 00 03 00 80 08 00 00 00 00
10: 04 70 31 df 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 d9 15 20 08
30: 00 00 00 00 40 00 00 00 00 00 00 00 ff 01 00 00
40: 10 80 92 00 01 80 00 10 20 08 04 00 00 00 00 00
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
60: 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
80: 01 8c 03 00 00 00 00 00 00 00 00 00 05 00 81 01
90: 04 00 e4 fe 00 00 00 00 21 40 00 00 00 00 00 00
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 00 00 01 00 10 00 10 80
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

# lspci -xxx -s 00:1f.3
00:1f.3 SMBus: Intel Corporation Atom processor C2000 PCU SMBus (rev 03)
00: 86 80 3c 1f 03 00 98 02 03 00 05 0c 00 00 00 00
10: 00 40 31 df 00 00 00 00 00 00 00 00 00 00 00 00
20: 01 e0 00 00 00 00 00 00 00 00 00 00 d9 15 20 08
30: 00 00 00 00 00 00 00 00 00 00 00 00 ff 02 00 00
40: 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
60: 03 04 04 00 00 00 08 08 00 00 00 00 00 00 00 00
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
80: 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
f0: 00 00 00 00 00 00 00 00 00 0f 02 01 03 03 03 00