Re: AES assembler optimizations

[Bill Davidsen <davidsen@tmr.com>]

David S. Miller wrote:

> On sparc64, we:
> 
> 1) Always save the full FPU state at context switch time if it
>    is active.
> 
> 2) On entry to a FPU-using kernel routine, we save the FPU if
>    it is active.
> 
> 3) On exit from a FPU-using kernel routine, we do nothing
>    except mark the FPU as inactive.
> 
> 4) FPU-disabled traps by the user restore the state saved
>    by #1 or #2

Depending on the cost saving of not saving the registers if they haven't 
changed, vs. the time to take the trap and set the FPU active again, it 
might be a win overall, even if you never used FPU in the kernel. Wasn't 
there a change between saving everything and saving FPU only when used 
"back when?" I seem to remember something about that, and the cost of 
the test vs. the cost of just doing the save.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me