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SubjectRe: [patch 2.6.13-rc3a] i386: inline restore_fpu

On Fri, 22 Jul 2005 at13:27:56 +1000, Andrew Morton wrote:

> hm. What context switch rate is that thing doing?

23000 - 25000 / second. I guess that explains why my attempt to
duplicate this in C failed -- it switches at 15-19 times per second:


/* i387 context switch benchmark
* compile this program without optimization
*/
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <sched.h>

int lo = 0, fp = 0, af = 0;
long i, iters;
pid_t child;
cpu_set_t cpuset;

void handler(int sig) {
lo = 0; /* stop looping */
}
struct sigaction sa = {
.sa_handler = handler,
};
main(int argc, char *argv[]) {
if (argc < 2) /* mandatory loop iteration count */
exit(1);
iters = atol(argv[1]);
if (argc > 2) /* loop in parent while waiting for child to exit */
lo = atoi(argv[2]);
if (argc > 3) /* use FP while wait-looping */
fp = atoi(argv[3]);
if (argc > 4) /* use cpu affinity -- all code runs on cpu 0 */
af = atoi(argv[4]);

__CPU_SET(0, &cpuset);

child = fork();
if (child) { /* parent */
if (af)
sched_setaffinity(0, &cpuset);
if (lo) {
sigaction(SIGCHLD, &sa, NULL);
if (fp)
__asm__ __volatile__("fld1" "\n\t" "fldz");
while (lo)
if (fp)
__asm__ __volatile__(
"fadd %st(1), %st(0)");
} else
wait(NULL);

} else { /* child */
if (af)
sched_setaffinity(0, &cpuset);
__asm__ __volatile__("fld1" "\n\t" "fldz");
for (i = 0; i < iters; i++)
__asm__ __volatile__("fadd %st(1), %st(0)");
}
}


> Is the benchmark actually doing floating point stuff?

They only release .class files. ISTR java does FP math even when
developers think they are doing integer math but I can't find any
references.

__
Chuck
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