Re: [patch 0/2] sLeAZY FPU feature

[Chuck Ebbert]

In-Reply-To: <1151782942.3195.56.camel@xxxxxxxxxxxxxxxxxxxxx>

On Sat, 01 Jul 2006 21:42:22 +0200, Arjan van de Ven wrote:

> > What sort of test?
>
> the one I did was long running FPU app (calculating PI using FPU)

Mine was just running a program that loops doing getpid() in one window
and this in another:

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>

#define rdtscll(t)      asm("rdtsc" : "=A" (t))

int main(int argc, char * const argv[])
{
        long long tsc1, tsc2;
        long double ld = 0.0;
        int i, iters = 999999999;

        rdtscll(tsc1);
        for (i = 0; i < iters; i++)
                ld += 1.0;
        rdtscll(tsc2);

        printf("count: %Lf, clocks: %llu\n", ld, tsc2 - tsc1);

        return 0;
}

So the ~0.4% gain I saw (averaging 10 tests) was likely the minimum
and Arjan's 8.5% gain when switching tasks after every FPU operation
is the max.

-- 
Chuck
 "You can't read a newspaper if you can't read."  --George W. Bush
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