Re: AES assembler optimizations

[Bill Davidsen]

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@xxxxxxx)
"The secret to procrastination is to put things off until the
 last possible moment - but no longer"  -me
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