Re: [Algorithms] Threading by software emulation

[Jon W. <hp...@mi...>]

Sebastian Lucas wrote:
> Each 4000 instructions I was switching them in this way:
> 1) Save the current registers, pc to the current thread.
> 2) Stop the current thread.
> 3) Find another one.
> 4) Copy the registers, pc to the cpu module.
> 5) Make it the current one.
> 6) Continue until we reach again the 4000 instructions executed.
>

I think 4000 instructions is way too often for good performance. Try 
switching every 100,000 or even every 500,000 instructions, in addition 
to explicit switching if there's a blocking call. I don't know the exact 
behavior of the PS/2 scheduler, though, so perhaps that won't be 
compatible, but I would assume you want to run until you block in most 
cases.

Also, I would implement context switch by storing PC, registers and 
other state in a struct, and allocate a new struct for each thread 
context. Instead of copying the context around, I would just use a 
pointer to the current context, and set that pointer to point to another 
context. Given that you probably are using a pointer to the current 
context anyway, that should not introduce any overhead in the innards of 
the emulator (other than host CPU cache misses on switch).

Sincerely,

jw