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Re: Sleazy FPU optimization

On Mon, Feb 11, 2008 at 07:44:39PM +0000, David Laight wrote:
> 1) Why would using printf for integers need the fpu

va_list processing and on-stack float values.

> 2) a fair number of context switches don't end up in userspace (or
>    only return there for a veru short time) doing a full FP save/restore
>    on these is likely to be expensive.

I am not saying to always *restore* the FPU. That should be evaluated,
but if the FPU was used, save it.

> 3) I suspect that some programs (like make) hardly ever use the FPU at all,
>    but will do a lot of context switches.

If a program doesn't use the FPU, it doesn't need it saved.


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