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SubjectRe: Linux 3.1-rc9
On Mon, 17 Oct 2011, Ingo Molnar wrote:
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
> For the record, i absolutely hate much of the other time related type
> obfuscation we do as well.
>
> For example the ktime_t obfuscation - we only do it to avoid a divide
> on 32-bit architectures that cannot do fast 64/32 divisions ...
>
> It makes the time code a *lot* less obvious than it could be.
>
> I think we should use one flat u64 nanoseconds time type in the
> kernel (preparing it with using KTIME_SCALAR on all architectures for
> a release or so), used with very simple and obvious C arithmetics.

It'd be nice, but this simply will not fly.

> That simple time type could then trickle down as well: we could use
> it everywhere in kernel code and limit the hodge-podge of ABI time
> units to the syscall boundary. (and convert the internal time unit to
> whatever ABI unit there is close to the syscall boundary)
>
> There's a point where micro-optimized 32-bit support related
> maintenance overhead (and the resulting loss of
> robustness/flexibility) becomes too expensive IMO.

That's not a micro optimization, it's a massive performance hit if you
force those 32bit archs to do 64/32 all over the place.

Thanks,

tglx


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