Re: Interesting scheduling times

Linus Torvalds (torvalds@transmeta.com)
Fri, 18 Sep 1998 21:21:45 -0700 (PDT)

On 19 Sep 1998, Andi Kleen wrote:
>
> Lazy FPU saving is pretty useless as long as glibc initialises the FPU
> in the startup code in every program. I do not know if you have seen Jakub
> Jelinek's AT_FPUCW patch - which passes the initial FPU state in the ELF
> auxilliary vector so that the startup code could decide if it needs to
> initialise the state or not. Without that the FPU initialisation makes
> lazy FPU saving useless.

No, the lazy FPU save works perfectly fine even with FPU initialization.
It does it lazily on a per-scheduling-quantum issue: if the process
doesn't use the FPU within some quantum, it will not save the FPU state.

As to the AT_FPUCW patch, I don't see the point in saving a constant value
in the ELF headers. Linux initializes the FPU for each process at
"exevce()" time, and glibc might as well depend on that instead of trying
to do so itself.

Linus

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