Re: [boost] units: performance testing

From: Steven Watanabe (steven_at_[hidden])
Date: 2007-03-29 23:37:17

Martin Schulz <Martin.Schulz <at> synopsys.com> writes:

> That gives:
> f3(x,y,z) took 1.515 seconds to run 1e+009 iterations with double =
> 2.64026e+009 flops
> f3(x,y,z) took 4.656 seconds to run 1e+009 iterations with
> quantity<double> = 8.59107e+008 flops
> 
> 2.6 GFlops? That is ok for a single thread. But the zero-overhead
> appears to be a factor of 3 now!
> 

Really? I get
f(x,y,z) took 1.953 seconds to run 1e+009 iterations with double = 2.04813e+009
flops
f(x,y,z) took 1.906 seconds to run 1e+009 iterations with quantity<double> =
2.09864e+009 flops

I am compiling with /Ox

the innermost loop is identical for the
double and quantity versions:

        sub	eax, 1
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        fadd	ST(0), ST(1)
        jne	SHORT $LN17_at_f

Obviously the compiler is cheating.

In Christ,
Steven Watanabe