6 May
2008
6 May
'08
5:20 a.m.
On Tue, 2008-05-06 at 00:24 +0200, Fons Adriaensen wrote:
After each iteration, call an empty function,
separately compiled,
that takes all three vectors as arguments (and _not_ as const *
of course). No more tricks. The overhead is peanuts compared
to the calculation.
You mean like this:
// defined in empty.c as return 0;
extern int empty(void*a,void*b,void*d);
And then call it at the end of iteration:
for (j = 0; j < n; ++j)
{
for (i = 0;i < N; ++i)
cxD[i]+= cxA[i]*cxB[i];
empty(&cxA,&cxB,&cxD);
}
fprintf (stderr,"> clock: %d ms %s\n",(clock()-clk)/1000,s);
Well, that certainly did level out everything. For n = 1000:
clock: 64680 ms (_Complex)
clock: 61990 ms (cvec_t)
clock: 71060 ms (original float array[N][2])
This measures the terrible latency I have between main memory and cache.
Changing back N from (1024 * 1024) to
#define N 1024
.. and then increasing n to a million again (this should be safe now?) -
so we can pretend not to be limited by PC100 - yields with icc:
clock: 16510 ms (_Complex)
clock: 6090 ms (cvec_t)
clock: 12800 ms (original float array[N][2])
.. and with gcc:
clock: 13820 ms (_Complex)
clock: 6330 ms (cvec_t)
clock: 13420 ms (original float array[N][2])
Very even I would say.