Re: Linux 3.1-rc9

[Ingo Molnar]

* Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:

> > 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.

Do we have some hard data on this, which we could put into comments 
in include/linux/ktime.h and such? Older versions of GCC used to do a 
bad job of long long handling on 32-bit systems - that might be a 
factor in the performance figures.

But i suspect you are right that the cost is still very much there 
...

Thanks,

	Ingo
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