[BUG] Extreme lag in FreeBSD 2.1.x

[win2kgamer]

In PCem v15 as well as PCem-dev commit 6bd1c70, FreeBSD 2.1.x lags/appears to hang after hardware probing. This only occurs on Pentium motherboards (The Intel Advanced/ZP and Shuttle HOT-557 were tested):

FreeBSD21_PCemv16.png (63.37 KiB) Viewed 4577 times

PCem hardware configuration (v15/dev - broken):
Machine: [Socket 7] Shuttle HOT-557
CPU: Intel Pentium 133
Memory: 16MB
Video: Phoenix S3 Trio64
HDD: 800MB IDE
FDD: 3.5" 1.44MB
CD-ROM: 4x PCemCD
Mouse: PS/2 (Microsoft 2-button serial was also tested)

PCem hardware configuration (v15/dev - working):
Machine [486] Award SiS 496/497
CPU: Intel 486DX4/100 (Recompiler enabled)
Memory: 16MB
Video: Phoenix S3 Trio64
HDD: 800MB IDE
FDD: 3.5" 1.44MB
CD-ROM: 4x PCemCD
Mouse: Microsoft 2-button serial

PCem hardware configuration (v14 - working):
Machine: [Socket 7] Award 430VX PCI
CPU: Intel Pentium 133
Memory: 16MB
Video: Phoenix S3 Trio64
HDD: 800MB IDE
FDD: 3.5" 1.44MB
CD-ROM: 4x
Mouse: PS/2

The "hang"/extreme lag occurs around this point in the kernel init/hardware probing:

Screenshot from 2020-03-12 23-32-58.png (9.62 KiB) Viewed 4577 times

Screenshot from 2020-03-12 23-33-12.png (11.31 KiB) Viewed 4577 times

Screenshot from 2020-03-12 23-33-18.png (10.15 KiB) Viewed 4577 times

EDIT: The IDE probe seems to work better in v14:

Screenshot from 2020-03-12 23-42-20.png (10.7 KiB) Viewed 4576 times

Performance stats when using the SiS 496/497:

FreeBSD21_PCemv16-working.png (59.02 KiB) Viewed 4576 times

EDIT: Updated title as I tested other 2.1.x versions (2.1.5, 2.1.6 and 2.1.7.1) and all of the 2.1 series is affected by this issue. 2.0.x and 2.2.x are not affected.

[win2kgamer]

I have performed some additional tests and found that the issue becomes a bit less severe (the keyboard response times are a bit shorter but still measured in seconds) when using the Adaptec AHA-1542 SCSI controller instead of IDE, the Tseng ET4000AX instead of an S3 Trio and disabling IDE in the BIOS.

EDIT: Performed some more tests on v16-dev using the Award SiS 496/497 machine and found that the OS works properly on the i486DX4/100 and Am486DX4/120 but the issue occurs on the Pentium OverDrive/63 and Am5x86/P75 CPUs. In v14, FreeBSD 2.1.x works correctly on all CPUs.

[win2kgamer]

Just tested v17-dev commit 302d05c and the issue still occurs.