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    SubjectDon't save registers during system calls
    There is currently an interesting thread on comp.arch discussing
    whether we really need to save registers during system calls. It seems
    that this is not requires and could save a few % on RISCs.

    In Linux, it seems like this means moving the register-saving from
    arch/*/kernel/entry.S to include/asm-*/system.h and the switch_to
    macro. In addition, you have to scramble clobber registers on exit
    from the kernel in entry.S, but that's a very fast operation. You only
    save registers when you switch the currently runnig task on a
    processor, not when crossing the kernel<->user-level boundary. This is
    only beneficial if the number of switches inside the kernel is lower
    than the number of system-calls which I assume is true. This isn't
    much point in doing on x86, but for RISCs and merced it could be


    Alexander Kjeldaas, Guardian Networks AS, Trondheim, Norway

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