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SubjectRe: [RFC][PATCH] linux-2.5.34_vsyscall_A0
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> agreed. Hear my idea:
>
> actually my idea on 64bit was to use the high 8 bit of each 64bit word to
> give you the cpuid, to get out the coherent data, including the sequence
> number that are read and written inversely with mb() like now (the
> sequence number as well will become per-cpu), so it is definitely doable
> without any single problem and in a very performant way, just not as
> easy as without the per-cpu info. Even if segmentation per-cpu tricks
> would be possible or available (remeber long mode is pure paging, no
> segmentation) it would be not worthwhile IMHO, the cpuid encoded
> atomically in each 64bit data provided by the vsyscall seems a much
> simpler and possibly more performant solution. You set a different
> per-cpu data-mapping with different pte settings in each cpu. The
> vsyscall bytecode remains the same, aware about this cpuid encoded in
> each 64bit word. Doing it in 32bit is ugly (or at least much slower)
> since most data is natively at least 32bit, it would need some slow
> demultiplexing.

At least on IA32 you could still use XCHG64 to atomically access the
values, but that always forces a write so it isn't cache friendly. Still
it probably is better than encoding the data in 32bit. It all depends
on how much data is needed.


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