CPU usage not improved

[yingemmachen]

Hi,

I used parallel_for in my visual c++ program. When I ran the program, the windows task manager showed that the total threads increased while the CPU usage did not change much (still about 15%).

Do you have any suggestion why this happens? My pc has intel core i7 CPU.

thanks,

Ying

[Dmitry_Vyukov]

Most likely something wrong with your program.
What exactly? There is a way too much variants to enumerate them all.

[ARCH_R_Intel]

You might try cutting your example down to something that you can post as an attachment in this forum, and see if anyone has ideas. Often when I'm cut ting down a problematic example, the root problem dawns on me before I'm even through cutting.

[yingemmachen]

Thanks.

My code is similar to the following. The structure is simple, but the function pParent->Calc is complicated, which calls some comercial library we bought without source code. Any suggestion is welcome and appreciated.


class ApplyCalc{
Parent *pParent;
int index;
double *result;
public:
void operator() ( const blocked_range& r ) const {
for (int j = r.begin(); j != r.end(); ++j) {
result = pParent->Calc(j,index)
}
}
ApplyCalc(Parent *pParent, int index, double *result) :
pParent(p), index(i), result{ }
};

void calcResult(double **allResult) {

for (i=0; i Parent *pParent;
int index;
pParent = getParentFromChildID(pAllChildren->getID(),
pAllParents,
numParents,
&index);
double *result = new double[NUMRUN];
parallel_for(blocked_range(0,NUMRUN),
ApplyCalc(pParent,index,result));
for (j=0; j {
allResult[i,j]=result;
}
delete[] result;
}
}

[Dmitry_Vyukov]

Try to apply parallel_for to the *outer* loop.
You call pParent->Calc() in parallel. Even if it's thread-safe, most likely it's uses mutexes which kills scalability.
Parallelization of outer loops is always preferable. That will also increase granularity and locality.