Re: [RFT] Port 0x80 I/O speed

["H. Peter Anvin" <hpa@zytor.com>]

Rene Herman wrote:
> On 12-12-07 01:09, Alejandro Riveira Fernández wrote:
>
> > > >  On my AMD 3800 X2 (2000MHz) ULi M1697 2.6.24-rc5 i get:
> > > >
> > > >  cycles: out 1844674407370808, in 1844674407369087
> > > >  
> > > > It is not constant but variations are not significant afaics
> > > Eh, oh, I guess you need to compile as a 32-bit binary...
> >  
> >  I tried without -O2 as Nigel Cunningham...
> >
> >  cycles: out 1562, in 865
> >  cycles: out 1562, in 866
> >  cycles: out 1555, in 858
> >  cycles: out 1562, in 866
> >  
> >  With -m32 -O2
> >  cycles: out 1566, in 876
> >  cycles: out 1555, in 865
> >  cycles: out 1594, in 931
> >  cycles: out 1559, in 874
>
> Great, thanks much for reporting. Sort of interesting in itself that 
> without -O2 you do still get correct results on 64-bit but for some 
> other time.
>
> You're the first one to go significantly below 1 us it seems.

Make sure the CPU is actually running at full frequency.

It probably would have been better to have used gettimeofday() around a 
sufficiently big loop, so that we would have gotten wall time rather 
than cycles.

	-hpa
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