Hello,
I am trying to understand some performance problems I ran into on my
xenomai system.
The testcode I attached performs a syscall(gettimeofday). Measuring time on
a vanilla Kernel gives the following output:
ticks for ppc_getccounter: 116, for gettimeofday: 1479
The same kernel with xenomai patched in gives this:
ticks for ppc_getccounter: 116, for gettimeofday: 4278
Is this the expected behaviour? Why is the time for a system call nearly 3
times as much?
#include <stdio.h>
#include <sys/time.h>
#include <time.h>
static void
ppc_getcounter(unsigned long long *v)
{
register unsigned long tbu, tb, tbu2;
loop:
asm volatile ("mftbu %0" : "=r" (tbu) );
asm volatile ("mftb %0" : "=r" (tb) );
asm volatile ("mftbu %0" : "=r" (tbu2));
if (__builtin_expect(tbu != tbu2, 0)) goto loop;
/* The slightly peculiar way of writing the next lines is
compiled better by GCC than any other way I tried. */
((long*)(v))[0] = tbu;
((long*)(v))[1] = tb;
}
int main(int argc, char* argv[])
{
while(1) {
struct timeval tv;
unsigned long long count0, count1, count2;
ppc_getcounter(&count0);
ppc_getcounter(&count1);
gettimeofday(&tv, NULL);
ppc_getcounter(&count2);
printf("ticks for ppc_getccounter: %lld, for gettimeofday:
%lld\n",
count1 - count0, count2- count1);
sleep(1);
}
}
Cheers
--
Dirk Eibach
Entwicklung
Guntermann & Drunck GmbH Systementwicklung
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