How to speed up simple Fortran OpenMP? -

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i have simple fortran program in main component 4-core openmp portion calculates dot product 

omp_num_threads=4 ... 30 k=1,lines   co(k)=0   si(k)=0   co_temp=0   si_temp=0  !$omp parallel private(dotprod,qcur) reduction(+:co_temp,si_temp)     40 i=1,ion_count       dotprod=(rx(k)*x(i)+ry(k)*y(i)+rz(k)*z(i))*((2*3.1415926535)/l)       co_temp=co_temp+cos(dotprod)*26 !qcur/qavg       si_temp=si_temp+sin(dotprod)*26 !qcur/qavg      40 continue  !$omp end parallel    co(k)=co_temp   si(k)=si_temp    q(k)= ( co(k),-si(k) )   s(k)= s(k) +( q(k) * conjg(q(k)) )   r(k)=r(k)+q(k) 30 continue

i'm not experienced fortran or optimization. i'm using xlf90_r file -qsmp=omp compile. 1/2 speedup when using 4 cores, else using c has gotten perfect 1/4 speedup doing same computation. same amount of time whether omp loop on 30 or 40. time around loop 30 program whole , loop takes 99.x% of time, i'm pretty sure bit bottleneck. egregious slow mistakes i've made in portion sees?

at quick glance @ code, looks each iteration of outer loop independent. make parallel loop not inner loop.

omp_num_threads=4 ... !$omp parallel private(dotprod,qcur,co_temp,si_temp) 30 k=1,lines   co(k)=0   si(k)=0   co_temp=0   si_temp=0    40 i=1,ion_count     dotprod=(rx(k)*x(i)+ry(k)*y(i)+rz(k)*z(i))*((2*3.1415926535)/l)     co_temp=co_temp+cos(dotprod)*26 !qcur/qavg     si_temp=si_temp+sin(dotprod)*26 !qcur/qavg   40 continue    co(k)=co_temp   si(k)=si_temp    q(k)= ( co(k),-si(k) )   s(k)= s(k) +( q(k) * conjg(q(k)) )   r(k)=r(k)+q(k) 30 continue !$omp end parallel

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