the v86-64 patch, Allows you to enter v86 mode from long mode on a 64bit linux kernel.
Basically it works just like an old school DOS Extender, where it’ll switch from long mode, to 32bit compatible mode, then enter v86 mode run some code, then re-enter 32bit mode, to jump back into 64bit long mode.
From an old mailing list:
PERFORMANCE This 64-bit DOSEMU compile runs substantially slower than the 32-bit compile that I used previously on this computer. I have several rather large PowerBASIC/DOS programs that are, in fact, the main reason why I use DOSEMU. Up until a couple of days ago, I had Fedora 7/i386 on this computer. I just happen to still have the numbers when compiling one of those programs with PowerBASIC/DOS under DOSEMU: With F7/i386: 1686600 lines per minute -- total time to compile the program: 0.2 seconds With F8/x86_64: 230400 lines per minute -- total time to compile the program: 1.6 seconds. The F8/x86_64 DOSEMU is running approximately 13 times slower. Which I bet runs a bit faster than an old 386.