Messages in this thread | | | Date | Sat, 19 Sep 1998 06:52:34 +0200 | From | Andi Kleen <> | Subject | Re: Interesting scheduling times |
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On Sat, Sep 19, 1998 at 06:21:45AM +0200, Linus Torvalds wrote: > > > 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.
Thank you for the clarification. Seems I was misunderstanding the used algorithm.
> > 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.
The problem is only that Ulrich Drepper does not trust the kernel to always keep the same value (this was the outcome of a discussion on l-k a few months ago). If the constant value was passed he could verify it and satisfy his paranoia @)
-Andi
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