I prefer,

reload equ -100
...
mov th0,#reload
mov tl0,#reload
...

The autoreload mode assures an average time between interrupts of 100 us (12 MHz clock), but the exact time may vary slightly depending on which instruction is being executed when the timer overflows (MULT and DIV are the longest).
In other words, the time deviation between interrupts is not accumulative. This makes a difference with respect to a SW reload scheme, where the error is summed.

Alfredo.